GB2236603A - Establishing a clock in the I/O card of a personal computer - Google Patents

Abstract

A clock for the UART circuit 32, 65 provided in a standard I/O card 30 or in a combined graphic card and I/O card 60 is derived, e.g. by frequency division, from the clock of the main board of a personal computer or from the clock 63 for a graphic data processing circuit 62, thereby eliminating the need for an independent crystal for the UART circuit 32. <IMAGE>

Description

METHOD OF ESTABLISHING A CLOCK IN THE I/O CARD OF A PERSONAL COMPUTER The present invention relates to a method of establishing a clock in -the I/O card of a personal computer and more particularly to a method of establishing a control clock in the UART of the I/O card of a personal computer.

Conventional I/O cards of a personal computer usually include means for receiving data bits from the central processing unit and transmitting the same to the desired peripheral equipment. This circuit element, included in a standard I/O card, was first developed by Intel Inc. and is referred to as the Universal Asynchronized Receiver and Transmitter, commercially abbreviated as UART. A traditional I/O card of this type is schematically shown in Figure 1. The I/O card 10 includes a UART circuit 11 which is operated at a frequency of 1.8432 MHz. This I/O card 10. is used with a PC/AT having a connection slot which provides a clock from the main board to the I/O card through the connectors 13 thereon. The clock of the main board operates at a frequency of 14.31818 MHz.

A conventional and typical combined graphic and I/O card is schematically shown in Figure 2. The card 20 includes all the circuit elements of a standard I/O card represented by block 21 and operates according to a clock generated by the crystal 22 at a frequency of 1.8432 MHz. Another graphic data processing circuit 23 is also included in the card 20 and operated according to another clock generated by a second crystal 24 at a frequency of 16 MHz.

From the above described conventional I/O cards used in a PC/AT, an independent crystal has been used to generate a control clock for the UART circuit on the I/O card. For the purpose of reduction of the manufacturing cost of an interface I/O card and to the same pin count, the crystals for the UART circuit can possibly be eliminated.

It is therefore the main object of the present invention to provide a method of establishing a clock in the I/O card of a personal computer without the need of an independent crystal.

The method of establishing a control clock in the I/O card of the present invention comprises a first step of directly impressing the clock from the main board of a personal computer on the I/O card thereof, a second step of processing the main board clock to achieve a desired clock for the UART circuit of the I/O card, and a third step of inputting the desired clock into the UART circuit of the I/O card.

In an alternative embodiment of the method of the present invention, the method comprises a first step of processing the clock from the graphic processing circuit to result in a desired clock for the UART circuit of the I/O card, and a second step of impressing the obtained clock on the UART circuit of the I/O card.

It is readily apparent that the advantage of the method according to the present invention is to save the cost of providing an independent crystal for the UART circuit. The resulting clock, obtained either from the main board clock or the control clock of the in the preferred embodiment graphic processing circuit, is a desired clock having frequency distortion of less than 0.5%.

The step of processing the clock either from the main board of the personal computer or from the graphic in the preferred embodiment data processing circuit means, is achieved 1 by a frequency dividing circuit means which will accurately result in desired clock for the UART circuit, which has a frequency of about 1.8432 MHz.

These and other objects, features and advantages of the method according to the present invention will become apparent from the following detailed description of the preferred embodiment with reference to the accompanying drawings.

Figure 1 is a schematic view of a standard I/O card for a personal computer.

Figure 2 is a schematic view of a conventional combined graphic card and I/O card for a personal computer.

Figure 3 is a schematic view of an I/O card impressed with a control clock for the UART circuit which was obtained from the clock of the main board of the personal computer according to the present invention.

Figure 4 is a circuit diagram of the frequency dividing circuit means used in the method of the present invention.

Figure 5 is a wave form diagram of various junctions of the frequency dividing means.

Figure 6 is a schematic view of a combined graphic card and I/O card with a processed clock for the UART circuit obtained from the clock of the graphic data processing circuit according to the method of the present invention.

Figure 7 is a frequency distortion list of the clock for the UART circuit impressed on the I/O card and obtained from the clock of the main board of a personal computer.

Figure 8 is a frequency distortion list of the processed clock for the UART circuit in the I/O card obtainea from the clock of the graphic data processing circuit.

Referring to Figure 3, which shows a schematic view of an I/O card adopting the method of the present invention, the I/O card 30 includes a connector 31 to be inserted into the slot of the main board of a personal computer, a UART circuit 32 for receiving and transmitting data bits and a frequency dividing circuit means 33. The clock of the main board of the personal computer operates at a frequency of 14.31818 MHz which is fed through the connector 31 to the frequency dividing circuit means 33.

The actual circuit embodying the frequency dividing means 33 is shown in Figure 4 . Referring to Figure 4 with reference to Figure 5 which is a wave form diagram at various junctions of the circuit, the frequency dividing means 33 functions as a frequency converting circuit. The impressed clock of the main board of a personal computer has a frequency of 14.31818 MHz which is processed by the frequency dividing means 33 to result in a clock with a frequency of 1.8475 MHz. The impressed 14.31818 MHz clock is first multiplied to result in a pulse signal at junction (A) with a frequency of 28.63636 MHz. The pulse signal at junction (A) is fed to an XOR gate which is controlled by the output of circuit Q6 to result in an inverse wave form at junction (B).Circuits Q1, Q2, Q3, Q4 are standard frequency dividing circuits, each of which divide the original frequency by two. A fifth and a sixth circuit Q5, Q6 form a latch circuit. Each time the fifth circuit Q5 counts to the 31st wave of the pulse signal at junction (B), as represented by the letters (E) and (F) in Figure 5, all the standard frequency dividing circuits Q1 to Q4 will be reset and the pulse signal at junction (B) will be reversed. Therefore, the obtained output pulse signal at junction (C) will have a frequency signal equal to 14.31818 MHz x 2 / 15.5 = 1.8475 MHz.

Referring again to Figure 3, the resulting clock signal with a frequency of 1.8475 MHz-is input into the UART circuit 32. It is noted that the clock for a standard #I/O card is designed to be 1.8432 MHz.

Therefore, the frequency distortion will be 0.23%. The frequency distortions have been tested to determine various desired baud rates for the UART circuit 32. The frequency distortions are listeo in the table shown in Figure 7. It is concluded that the tested frequency distortions are acceptable for the operation of the UART circuit 32.

Another embodiment of the method of the present invention can be understood with reference to Figure 6, which shows a schematic view of a combined graphic card and I/O card. The card 60 has a connector .61 to be connected to the main board of a personal computer, a graphic data processing circuit 62 operated according to the clock generated by a crystal 63, a frequency conversion circuit means represented by an empty square 64, and a UART circuit 65. The clock signal for the UART circuit 65 impressed on the combined graphic card and I/O card is obtained from the clock of the graphic data processing circuit means 62. It is known that the crystal 63 will generate a clock with a frequency of 16 MHz. The frequency conversion circuit means 64 will then convert the input 16 MHz signal into a clock for the UART circuit 65 with a frequency of 1.84615 MHz.

The actual logic circuit for such a frequency conversion can be achieved by one skilled in the art.

The logic circuit functions at a frequency of 16 MHz x 3 / 26 = 1.84615 MHz. With such a circuit, the frequency distortion is 1.84615 MHz / 1.8432 MHz = 0.16%. The frequency distortions for various desired baud rates for the transmitting of data bits are listed in a table shown in Figure 8.

Claims (10)

CLAIMS:

1. A method of impressing a clock signal on a UART circuit (32) in an I/O card (30) used in a personal computer having a main board clock, comprising: a first step of impressing said main board clock on said I/O card (30); a second -step of processing said main board clock to obtain a control clock with a pre set frequency; and a third step of inputting said obtained control clock into the UART circuit (32) in the I/O card (30); thereby eliminating the use of an independent clock crystal for the UART circuit (32) in the I/O card (30).

2. A method as claimed in Claim 1 wherein said first step comprises the impressing of a main board clock with a frequency of 14.31818 MHz on the I/O card (30).

3. A method of impressing a clock on a UART circuit (65) provided in a combined graphic card and I/O card (60) used in a personal computer, said graphic card (60) including a graphic data processing circuit means (62) operated according to a graphic clock (63), comprising: a first step of processing said graphic clock (63) to obtain a control clock for said UART circuit (65), said control clock having a pre set frequency; and a second step of inputting said obtained control clock into said UART circuit (65) in said combined graphic card and I/O card (60); thereby eliminating the need for an independent clock crystal for said UART circuit (65) in said combined graphic card and I/O card (60).

4. A method as claimed in Claim 3 wherein said first step comprises the impressing of a graphic clock (63) of a frequency of 16 MHz to obtain a control clock for said UART circuit (65).

5. A method as substantially described hereinbefore with reference to the accompanying drawings.

6. An I/O card for a personal computer, the card carrying a UART circuit having a clock input, and the card further comprising a terminal for receiving the main board clock of the personal computer, and a frequency processing circuit for receiving the main board clock from said terminal, processing the main board clock and supplying the processed clock to the clock input of the UART circuit.

7. An I/O card for a personal computer, the card being substantially as herein described with reference to the Figures 3 to 5 of the accompanying drawings.

8. A combined graphic and I/O card for a personal computer, the card comprising graphic data processing circuit means having a clock terminal, a graphic clock for supplying a clock signal to said clock terminal of said graphic data processing circuit means, a UART circuit having a clock terminal, and frequency processing means responsive to said graphic clock for processing said clock and supplying the processed clock to said clock terminal of said UART circuit.

9. A combined graphic and I/O card for a personal computer, the card being substantially as herein described with reference to Figure 6 of the accompanying drawings.

10. A personal computer having a card as claimed in any one of claims 6 to 9.