US3561354A

US3561354A - Print hammer selection circuit in endless belt line printers

Info

Publication number: US3561354A
Application number: US752063A
Authority: US
Inventors: Jaroslav Mrkvicka
Original assignee: Vyzkumny Ustav Matematickych Stroju
Current assignee: Vyzkumny Ustav Matematickych Stroju
Priority date: 1967-08-10
Filing date: 1968-08-12
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09
Also published as: FR1573798A

Abstract

Staggered successions of reference character codes that are generated in timed relation to the periodic movement of a typecarrying belt past an aligned row of printing hammers are periodically sampled. The respective samples are routed through selected time slots of successive frames containing information character codes representative of the type characters to be printed. The occurrence of an identity between a shifted sample and the information character code in a particular time slot causes the actuation of an associated one of the printing hammers to print the corresponding type character.

Description

I United States Patent 1 1 3,56 1,354

[72] Inventor Jaroslav Mrkvicka [56] Referen e Cited l N f gg gz UNITED STATES PATENTS [2H P 3,066,601 12/1962 Eden 101 93 [22] F1Ied Aug. 12, 1968 3,289,576 12/1966 Bloom et a1 101/93 [45] Patented Feb. 9,1971 3 303 775 2/1967 101/93 [73] Assignee Vyzkumny ustav matematickych stroju lamiuzzl 3,312,174 4/1967 Cunn1ngham.. 101/93 Praha, Czechoslovakla, a fi 3 443 514 5/1969 Schwartz 101/93 [32] Priority Aug. 10, 1967 [33] Czechoslovakia Primary ExaminerWil1iam B. Penn [3 1 I PV5,76l-67 Attorney-Arthur O. Klein ABSTRACT: Staggered successions of reference character 54 PRINT HAMMER SELECTION CIRCUIT 1N g sf f i a the Q ENDLESS BELT LINE PRINTERS e en 0 a P Ty g e pas an a lgne row 0 pnn 4 Cl 6 D F mg hammers are periodically sampled. The respective samples films rawmg are routed through selected time slots of successive frames [52] US. Cl 101/93, containing information character codes representative of the 340/ 172.5 type characters to be printed. The occurrence of an identity [51] Int. Cl B41 j l/20, between a shifted sample and the information character code B41 j 9/ 14; 606k 15/08 in a particular time slot causes the actuation of an associated [50] Field of Search I01/93RC, one of the printing hammers to print the corresponding type 96RC; 340/1461, 236(Inquired), 172.5

character.

* PATENIED rm sla n sum u m 4 a iyf.

.% HMJH i WEWQEH I l s L c c C. C. L \L .L i?! fi 1!. 1.1V 1111 i T F TL,

JQ SIm'WR QKKA PRINT HAMMER SELECTION CIRCUIT IN ENDLESS BELT LINE PRINTERS BACKGROUND OF THE INVENTION One form of digitally controlled line printer employs an endless belt on which rows of successive type characters are suitably embossed. The belt moves periodically past a succession of aligned printing hammers whose spacing determines the column spacing of the printed line. The hammers are selectively actuated to press a pressure-sensitive paper tape against the oppositely disposed type character on the belt and thus provide a corresponding impression on the tape.

Each hammer is associated with a predetermined time slot in a recurrent frame of incoming data defined by a plurality of information character codes. The code occurring in each time slot determines the type character that is to be printed in the column defined by the corresponding hammer.

Actuation of the printing hammer associated with each time slot occurs in response to a detected identity, in such time slot, of the then occurring information character code and one of a plurality of reference character codes which are respectively representative of the successive type characters on the belt. The latter are generated by a suitable selection circuit actuated in synchronism with the periodic movement of the successive type characters on the belt past a fixed point.

In the past, selection circuits for moving-belt line printers have been complicated, particularly where the spacing between successive ones of the type characters on each row of the belt is different from the spacing between successive ones of the printing hammers.

SUMMARY OF THE INVENTION The present invention provides a relatively simple selection circuit for moving-belt line printers having a type spacing on the belt that is greater than the column spacing of the printed line by a factor K /Q where '70 is a rational number greater than 1 and where P and Q have no common factors. A character generator operating in MODULO-P fashion is coupled to the moving belt for generating P staggered but otherwise identical successions of the reference character codes corresponding to the successive typed characters on the belt. The successions of reference codes are sequentially sampled in successive ones of the frames. A shifting circuit routes each sample through an associated set of time slots of the corresponding frame; a separate set of time slots is assigned to each of the staggered successions of reference character codes. Each identity between a shifted sample and the simultaneously occurring information character code actuates the printing hammer assigned to the time slot in which the identity occurs.

BRIEF DESCRIPTION OF THE DRAWING The nature of the invention and its advantages will appear more fully from the following detailed description taken in conjunction with the appended drawing, in which:

FIG. 1 is a block and schematic diagram of a selection circuit for a digitally controlled line printer in accordance with the invention;

FIG. 2 is a set of waveform diagrams illustrating a frame of time slots coincident with those containing coded information for controlling the line printer of FIG. 1;

FIG. 3 is a pictorial diagram of one form of MODULO-P character generator suitable for use in the selection circuit of FIG. 1;

FIG. 4 is a set of waveform diagrams for the MODULO-3 character generator of FIG. 3;

FIG. 5 is a set of waveform diagrams for a shifting-pulse generator suitable for use with the selection circuit of FIG. 1, illustrating the time relation among the shifting pulses, the frame duration, and the waveforms of FIG. 4; and

FIG. 6 is a pictorial diagram of an alternative form of character generator for producing the waveforms of FIG. 4.

DETAILED DESCRIPTION Referring to the drawing. FIG. I illustrates a digitally controlled line printer 10 for printing a line of N type characters (not shown) on a pressure-sensitive paper web 2A. The printing of the line is accomplished with the use of N aligned. solenoid-actuated printing hammers 12-1. 12-2. IZ-N which selectively press the web 2 against an endless moving belt 11 on which axially disposed rows of typed characters -110 to be printed are embossed. The belt 11 is suitably driven by a pair of drive rolls 2IA-21A at constant speed for translational movement parallel to the hammers 12 to periodically move each successive type character through positions directly opposite each of the hammers l2.

The solenoids (not shown) of selected hammers 12 are actuated by energizing associated ones of a plurality of individual power supplies 9-1, 9-2, 9-N. The N power supplies 9, in turn, are energized by the application thereto of N command bits which are outpulsed over N channels 14-1, 14-2, l4-N of a serial-to-parallel converter 8. A predetermined state of each command bit (eg a binary 1) applied to the associated one of the power supplies 9 will actuate the hammer 12 associated therewith to print the type character on the then-opposed portion of the belt 11.

As is well known in the line printer art, the incoming information which controls the generation of the command bits for each line to be printed may be contained in successive recurrent frames each having a predetermined number of time slots of duration T. Each frame of information is generated by a suitable external source (represented by a computer I00) and stored in serial form in a suitable buffer memory 7 of conventional construction. For example, the buffer 7 may take the form of a delay line having a storage capacity of IT time slots as depicted in FIG. 2, wherein successive frames of the incoming information stored in the buffer may recur at intervals of length Z. Not all of the time slots in the buffer need be employed for information storage; as shown in FIG. 2, for example, the seventh time slot in each frame may be inactive for information storage purposes and may be used to store suitable error checking codes if desired.

As indicated below, the identification of an information character code occurring in a particular time slot by the line printer selection circuit (designated generally at 22A in FIG. 1) will provide the command bit for the associated hammer 12 to print the required type character. For this purpose the converter 8 is employed to relate the respective time slots to separate the ones of the channels 14 for individually exciting the associated hammer power supplies 9 in the manner described, e.g., in applicants copending application Ser. No. 729,825, filed May 16, I968, and entitled ERROR CHECKING CIRCUIT FOR DIGITALLY CONTROLLED PRINTERS."

It will be assumed for purposes of the following discussion of the selection circuit 22A that the spacing between successivetype characters on the belt 11 is lktimes the spacing K between the successive hammers 12.

The belt 11 is mechanically coupled, as by a link 11A, to a character generator 1. As shown in FIG. 3, the generator I may illustratively comprise a rotatable disc 15 which makes one revolution for each increment of belt movement equal to the spacing between successive type characters thereon. The disc 15 has a first track 151 that cooperates with a first pickup 161 to provide, during each revolution, an output pulse having a duration proportional to one-third of the spacing between successive type characters on the moving belt 11. Each pulse from the pickup 161 is applied to the input of a MODULO 3-counter 16 having three outputs in the form of staggered but otherwise identical first pulse trains at, B and 7 (FIG. 4). Each of the trains (1,3, 'y has a period T-{proportional to the belt type spacing, and a pulse duration corresponding to onethird of such spacing.

Referring again to FIG. 3, the first pulse trains 01.13, and which appear on output lines 101, I02. and 103 of the counter 16, are applied to separate inputs of a triggcrable character register 17 which provides three staggered but otherwise identi cal successions Da, DB. and D-y (FIG. 4) of reference character codes in respective. synchronism with the pulse trains 'y, B, and a. Each of the reference codes in the successions Da, DB, and D7, which are individually outpulsed over

lines

111, 112, and 113 of the register 17, corresponds to (and is represented in FIG. 4 by a line labeled as) one of the successive type characters on the belt 11. The construction of such a character register, which provides a different code on its output each time it is triggered, is well known in the art and will not be further discussed here. The basic triggering signals for the register 17 are applied once during each cycle of revolution of the disc 15 (FIG. 3) by a pickup 171 associated with a suitable second track 152 on the disc 15, while the staggered pulse trains 'y, B, and a are used to operate the register 17 in MODULO-3 fashion similar to that of the counter 16.

Referring again to FIG. 1, the respective successions of reference character codes outpulsed by the generator 1 over the

lines

111, 112, and 113 are sampled at the beginning of each frame of information stored on the buffer 7 by means of pulses from a sampling pulse generator 2. (For purposes of the following discussion the frame length Z may be taken to coincide with the pulse length T 2/3 of each of the trains at, B, and y in the manner shown in FIG. 5.) The generator 2 (FIG. 1) may be a MODULO-3 counter of the same general type as the counter 16 of FIG. 3, except that the generator 2 is triggered at time slot intervals T rather than at intervals proportional to T 2/3, as was the case with the counter 16. Thus, the generator 2 provides, on

output lines

21, 22, and 23, three staggered second pulse trains a, b, and c (FIG. 2) each of which has a pulse length T. The triggering pulses for the generator 2 (FIG. 1) are obtained from the computer 100 over a line 20.

The generator 2 also provides a timing pulse over an output line 24 to define a sampling interval equal to 3T at the beginning of each frame in the manner shown in FIG. 2.

The reference code successions Da, DB, and D-y on the lines 111, 112, and 113 (FIG. 1) are respectively applied to

first inputs

411, 421, and 431 of a plurality of

sampling gates

41, 42, and 43. The second pulse trains c, b, and a are respectively applied to

second inputs

413, 423, and 433 of the gates 41-43. The timing pulse Q is applied in common to

third inputs

412, 422, and 432 of the gates 41-43. With this arrangement, the respective character code sequences Da, DB, and U are sampled during successive ones of the first three time slots of successive frames of the information stored in the buffer 7.

The samples of the sequences Du, DB, and By are applied, via

lines

414, 424, and 434 to

inputs

441, 442, and 443 of an OR gate 44. The successive samples at the output of the OR gate 44 are applied to an input 51 of a suitable shift register 5. The register is adapted, in a conventional manner, to store each of the successive samples applied thereto from the OR gate 44 and thereafter, in response to a succession of pulses S (FIG. 5) applied thereto over an integral number of time slots, to shift the stored sample through the number of time slots occupied by the coincident pulse S.

The timing of the pulses S shown in FIG. 5 is chosen to suecessively shift each sample through a set of predetermined time slots uniquely assigned to the corresponding one of the reference code successions Dot, DB, and Dy. Such timing is effectively obtained with the use of a shifting pulse generator 3. The latter operates, in the manner described below, on the first and second staggered sets of trains at, B, and 'y and a, b, and 0 applied to inputs 34-36 and 31-33, respectively, of the generator 3. In particular the pulse sequence S results from the performance, in the generator 3, of the operation S= a(b+) B(a+) 'y(a+). The generator 3 also provides a succession of gating pulses T. The pulses T result from the performance, in the generator 3, of the operation T at: Bh yc and so are complementary to the pulses S,

as clearly shown in FIG. 5. The pulses T are used to selectively open a second gate 55 (FIG. 1) through a control input 552. During each open period of the gate 55, the then-occurring shifted sample in the register 5 is transmitted to a first input 61 of a conventional coincidence decoder 6.

The manner in which the successive samples may be shifted through predetermined time slots of successive frames will now be illustrated. It will be noted from FIG. 5 that the first time slot in the first depicted frame. i.e., that corresponding to the pulse duration of the first train a, manifests the absence of a pulse S and the presence ofa pulse T. Thus, in this first time slot, the sample of the reference code sequence Da applied to and stored in the register 5 (FIG. 1) remains unshifted and is directly applied in the first time slot to the coincidence decoder 6 through the now-enabled gate 55. Because of the presence of the pulse S (FIG. 5) in the second and third time slots in that frame, the next outpulsing of the sample of the sequence Da to the decoder 6 occurs, during the fourth time slot, through the gate 55 which is open by virtue of the simultaneous presence of the pulse T. During the fifth and sixth time slots, the pulse S occurs again, so that (ignoring the depicted inactive time slot) the shifted sample is outpulsed, during the seventh active time slot in the frame, through the gate 55 which is again opened by the pulse T. Thus, a sample of the reference code sequence Da is applied to the input of the coincidence decoder 6 in synchronism with the pulses T, i.e. during the first, fourth, seventh etc. active time slots of the frame corresponding to the pulse duration of the sequence Da. In a similar manner, it will be noted from FIG. 5 that samples of the reference code sequence DB are applied, in synchronism with the pulses T, to the input of the coincidence decoder 6 during the second, fifth, eighth etc., active time slots of the frame corresponding to the pulse duration of the sequence DB. Finally, samples of the reference sequence D-y are applied to the input of the coincidence decoder during the third, sixth, ninth, etc., active time slots of the frame corresponding to each pulse duration of the sequence D The printing hammers 12 may be grouped in accordance with the time slots through which the samples of the successive reference code sequences are routed. In particular, the hammers associated with the first, fourth, and seventh columns of the line to be printed are controlled by the shifted samples of the sequence Dot. The hammers associated with the second, fifth, eighth, etc. columns are controlled by the shifted samples of the pulse sequence DB; and the hammers corresponding to the third, sixth, ninth, etc. columns are controlled by the shifted samples of the pulse sequence D-y.

The sequence of shifted code samples applied to the input 61 (FIG. 1) of the decoder 6 is compared with the information codes in the successive frames stored in the buffer 7 and applied to a second input 62 of the decoder 6. Within the decoder 6, comparison is made between the sample and the coincident information character codes in each of the time slots assigned to the corresponding one of the code sequences Da, DB and D As one typical example the shifted samples of the sequence Da are suitably compared with the contents of the first, fourth, seventh etc., time slots in the coincident frame of incoming information from the buffer 7. Each coincidence of the shifted sample and the information character code in one of the assigned time slots results in the generation of a command bit which is applied, through the associated channel 14 of the serial-to-parallel converter 8, to the power supply 9 of the associated printing hammer 12. The resulting actuation of the hammer solenoid causes a printout of the type character (on the belt 11) disposed opposite the excited hammer 12. It will be evident that excitation of the hammers associated with the code sequences DB and D may be accomplished in an analogous manner.

An alternative embodiment of the character generator 1 is shown in FIG. 6. This embodiment employs a rotatable disc 13 that is encoded, as by suitable apertures (not shown) thereon,

with the required reference character codes. The disc 13 is mechanically coupled. via the link 11A, for rotation once during each movement of the belt ll through the spacing between successive type characters Three

pickups

141, 142, and 143 are associated with respective points of the periphery of the disc that are spaced at intervals D. The distance D corresponds to 2/3 of the type spacing on the belt. In this embodiment, the pickups l4ll43 respectively outpulse both the staggered first trains a, B and 'y and the correspondingly staggered reference code sequences Du, DB and D'y. Details of the construction of the disc 13 and the pickups l4l-l43 are well known in the art and will not be discussed further here.

in the foregoing, the invention was described in connection with a preferred arrangement thereof. Many other variations and modifications will now become obvious to those skilled in the art. For example, it will be appreciated that the ratio of the spacing between successive type characters on the belt 11 and the successive hammers is not restricted to the factor 1.5, but may be any rational number P/Q greater than one, where P and Q have no common factor. In such a case it is necessary that the generators l6 and 2, which provide the first and second trains at, B, 'y and a, b, c, operate on a MODULOP basis, with P sampling gates being correspondingly required. In such a case the character generator embodiment shown in FIG. 6 would have a spacing D equal to Q/P times the type spacing of the belt 11. These and other modifications may be made without departing from the spirit and scope of the inventron.

l claim:

1. In a line printer whereina row of N aligned printing hammers cooperate with an endless type carrier that is disposed parallel to the row for movement past the row and wherein the type spacing on the carrier is greater by an indivisible rational factor P/Q than the spacing between adjacent ones of the hammers, an improved apparatus for selectively actuating the printing hammers in response to coded information characters grouped in successive incoming data frames of N active time slots each, which comprises:

a reference character generator having P outputs for separately providing P similar sequences of reference character codes individually corresponding to the successive types on the carrier, the character generator having P inputs respectively associated with the P outputs, each input being operable when excited for triggering the next reference code in the sequence on the associated output;

means coupled to the carrier for generating P first pulse trains in MODULO-P fashion at a rate proportional to the spacing of the successive types on the carrier;

first means for individually coupling the P first pulse trains to the P inputs of the character generator to respectively produce the reference character sequences in synchronism therewith;

a coincidence decoder having first and second inputs;

means synchronized with the occurrence of the successive data frames of coded information characters for cyclically gating, to the first input of the decoder, samples of each of the outputs of the character generator at intervals of P time slots and for a duration of one time slot, whereby the time slots occupied by the samples from each output of the character generator are mutually distinct;

means for applying the successive frames of coded information characters to the second input of the decoder;

a serial-to-parallel converter coupled to the output of the decoder and having N outputs corresponding to the N time slots of each data frame; and

second means for individually coupling the outputs of the converter to the printing hammers.

2. Apparatus as defined in claim 1, in which the generating means comprises, in combination, a disc rotatably coupled to the type carrier, the disc having first and second signal tracks; a first pickup device coupled to the first track for producing, during each revolution of the disc, a pulse having a duration corresponding to of the type spacing on the type carrier; a

MODULO-P counter coupled to the output of the first pickup device; and a second pickup device coupled to the second track for generating an impulse once during each revolution of the disc; and in which the first coupling means comprises means for transmitting the outputs of the MODULO-P counter and the second pickup device to the character generator.

3. Apparatus as defined in claim 1, in which the generating means comprises, in combination; a coded disc rotatably coupled to the type carrier, and at least a pair of pickup devices coupled to the periphery of the disc, the angular spacing between the pickups corresponding to Q/P times the distance between adjacent types on the type carrier.

4. In a line printer wherein a row of N aligned printing hammers cooperate with an endless type carrier that is disposed parallel to the row for movement past the row and wherein the type spacing on the carrier is greater by an indivisible rational factor P/Q than the spacing between adjacent ones of the hammers, an improved apparatus for selectively actuating the printing hammers in response to coded information characters grouped in successive incoming data frames of N active time slots each, which comprises:

a reference character generator having P outputs for separately providing similar sequences of reference character codes individually corresponding to the successive types on the carrier, the character generator having P inputs respectively asspCiated with the P outputs, each input being operable when excited for triggering the next reference code in the sequence on the associated output;

first means coupled to the carrier for generating P first pulse trains in MODULO-P fashion at a rate proportional to the spacing of the successive types on the carrier;

means for individually coupling the P first pulse trains to the P inputs of the character generator to respectively produce the reference character sequences in synchronism therewith;

second means operative in synchronism with each time slot in a data frame for generating P second pulse trains in MODULO-P fashion, each second pulse train having a pulse length equal to that of a time slot;

normally disabled first gates each having first and second inputs;

means for individually coupling the P outputs of the character generator to the first inputs of the first gates;

means for individually applying the P second pulse trains to the second inputs of the first gates;

means for opening the first gates during each frame for P time slots;

an OR gate coupled to the outputs of the first gate;

storage means including a shift register coupled to the output of the OR gate and having a control input, the presence of a pulse in a given time slot at the control input causing the register to shift to the next succeeding time slot;

a normally disabled second gate coupled to the output of the storage means and having a control input;

3, a coincidence decoder having first and second inputs; 5 2 means for coupling the output of the second gate to the first input of the decoder;

means responsive to the first and second pulse trains for generating third and fourth complementary pulse trains, the amplitude of the third pulse train being the sum of the products of the amplitudes of corresponding ones of the first and second pulse trains;

means for applying the fourth pulse train to the control input of the storage means;

means for applying the third pulse train to the control input of the second gate;

means for applying each data frame to the second input of the coincidence decoder;

a serial-to-parallel converter coupled to the output of the decoder; and

means individually coupling the outputs of the converter to the printing hammers.

Claims

1. In a line printer wherein a row of N aligned printing hammers cooperate with an endless type carrier that is disposed parallel to the row for movement past the row and wherein the type spacing on the carrier is greater by an indivisible rational factor P/Q than the spacing between adjacent ones of the hammers, an improved apparatus for selectively actuating the printing hammers in response to coded information characters grouped in successive incoming data frames of N active time slots each, which comprises: a reference character generator having P outputs for separately providing P similar sequences of reference character codes individually corresponding to the successive types on the carrier, the character generator having P inputs respectively associated with the P outputs, each input being operable when excited for triggering the next reference code in the sequence on the associated output; means coupled to the carrier for generating P first pulse trains in MODULO-P fashion at a rate proportional to the spacing of the successive types on the carrier; first means for individually coupling the P first pulse trains to the P inputs of the character generator to respectively produce the reference character sequences in synchronism therewith; a coincidence decoder having first and second inputs; means synchronized with the occurrence of the successive data frames of coded information characters for cyclically gating, to the first input of the decoder, samples of each of the outputs of the character generator at intervals of P time slots and for a duration of one time slot, whereby the time slots occupied by the samples from each output of the character generator are mutually distinct; means for applying the successive frames of coded information characters to the second input of the decoder; a serial-to-parallel converter coupled to the output of the decoder and having N outputs corresponding to the N time slots of each data frame; and second means for individually coupling the outputs of the converter to the printing hammers.

2. Apparatus as defined in claim 1, in which the generating means comprises, in combination, a disc rotatably coupled to the type carrier, the disc having first and second signal tracks; a first pickup device coupled to the first track for producing, during each revolution of the disc, a pulse having a duration corresponding to P of the type spacing on the type carrier; a MODULO-P counter coupled to the output of the first pickup device; and a second pickup device coupled to the second track for generating an impulse once during each revolution of the disc; and in which the first coupling means comprises means for transmitting the outputs of the MODULO-P counter and the second pickup device to the character generator.

3. Apparatus as defined in claim 1, in which the generating means comprises, in combination, a coded disc rotatably coupled to the type carrier, and at least a pair of pickup devices coupled to the periphery of the disc, the angular spacing between the pickups corresponding to Q/P times the distance between adjacent types on the type carrier.

4. In a line printer wherein a row of N aligned printing hammers cooperate with an endless type carrier that is disposed parallel to the row for movement past the row and wherein the type spacing on the carrier is greater by an indivisible rational factor P/Q than the spacing between adjacent ones of the hammers, an improved apparatus for selectively actuating the printing hammers in response to coded information characters grouped in successive incoming data frames of N active time slots each, which comprises: a reference character generator having P outputs for separately providing similar sequences of reference character codes individually corresponding to the successive types on the carrier, the character generator having P inputs respectively associated with the P outputs, each input being operable when excited for triggering the next reference code in the sequence on the associated output; first means coupled to the carrier for generating P first pulse trains in MODULO-P fashion at a rate proportional to the spacing of the successive types on the carrier; means for individually coupling the P first pulse trains to the P inputs of the character generator to respectively produce the reference character sequences in synchronism therewith; second means operative in synchronism with each time slot in a data frame for generating P second pulse trains in MODULO-P fashion, each second pulse train having a pulse length equal to that of a time slot; normally disabled first gates each having first and second inputs; means for individually coupling the P outputs of the character generator to the first inputs of the first gates; means for individually applying the P second pulse trains to the second inputs of the first gates; means for opening the first gates during each frame for P time slots; an OR gate coupled to the outputs of the first gate; storage means including a shift register coupled to the output of the OR gate and having a control input, the presence of a pulse in a given time slot at the control input causing the register to shift to the next succeeding time slot; a normally disabled second gate coupled to the output of the storage means and having a control input; a coincidence decoder having first and second inputs; means for coupling the output of the second gate to the first input of the decoder; means responsive to the first and second pulse trains for generating third and fourth complementary pulse trains, the amplitude of the third pulse train being the sum of the products of the amplitudes of corresponding ones of the first and second pulse trains; means for applying the fourth pulse train to the control input of the storage means; means for applying the third pulse train to the control input of the second gate; means for applying each data frame to the second input of the coincidence decoder; a serial-to-parallel converter coupled to the output of the decoder; and means individually coupling the outputs of the converter to the printing hammers.