GB1314024A - Communications systems - Google Patents

Abstract

1314024 Digital transmission systems; signalling by DC ULTRA ELECTRONICS Ltd 11 Sept 1970 [13 Nov 1969] 47290/69 Heading H4P Both data and clock pulses combined in a ternary signal, preferably RTZ, is transmitted over a two conductor transmission line 1, 2 by a pair of driver elements 6, 7 to a first differential comparator 8 giving an output representative of a first ternary state and second comparator 9 giving an output representative of a second ternary state and both comparator outputs representing the third ternay state with an OR gate delivering clock signals. The arrangement is stated to be uncritical of frequency or pulse width constancy and the bit rate need not be the same in each direction of transmission. Lines 1, 2 are separately pulsed by positive voltages corresponding to 1's and 0's respectively (see Fig. 5b, 5c, not shown) corresponding to signal pulses injected at D1 and gated by clock pulses P1 causing either receiver comparator 8 or 9 to give a corresponding negative output. Direction of transmission is controlled by a signal on C1 which prepares gates 11, 12 and inhibits receiving gates 29, 30 (or C2, 36, 37, 17 for reverse transmission). Diodes 15, 16, 38, 39 act as bias generators causing the -ve terminals to be about 1À4 volts more positive than the +ve terminal due to each line not in use providing a temporary bias source thus blocking noise below the bias threshold level. It is stated that reconstituted clock pulses P1 (IN) may be used to reconstitute data pulses D1 by clocking a shaft register into which SO1 and SO1 signals are passed; preferably however both SO1 and SZ1 signals are utilized, particularly for parity checking. The shunting effect of the low output impedance of the drivers at the receiving end, e.g. 13, 14 is eliminated by diodes 22, 23 and resistors 43, 44. The line conductors may be in the form of a twisted pair. The use of the arrangement may be extended by using coincident positive or negative pulses on the lines simultaneously and connecting an AND function between the lines at the receiving end but this is vulnerable to common mode noise. Another form of information can also be transmitted when it is not in use for the ternary RTZ signals or alternatively other information can be interposed between RTZ signals.