Patent GB-1491504-A (GB)
Title: Control circuit for local connection of a peripheral device for data transmission
IPC: G06F3/12
Filed: 1974-11-11
Abstract: 1491504 Data transmission HONEYWELL INFORMATION SYSTEMS ITALIA SpA 11 Nov 1974 [9 Nov 1973] 48765/74 Heading H4P The arrangement relates to a control circuit which comprises the separate functions of enabling local peripheral devices to communicate directly with a central processor in a "request and response" mode i.e. according to local timing parameters, also enabling communication with remote devices through modems in a continuous sequence in a synchronous mode with timing imposed by the control circuit. The control unit, which may be associated with a processor, is connectible through a transmission medium and modems to a remote peripheral device, which is interconnected via respective interfaces through which a modem signals its readiness to transfer data, with a second peripheral device connected to the same or another control unit associated with the processor through a local connection also including an interface. A means in the second peripheral is responsive to binary signals indicating that it is or not ready to accept further data, with a means connected to the local connection interface so as to apply the binary signals to that terminal on the data controller side of the interface which would receive a readiness signal if the control unit were in remote connection. The peripheral device may be a printer and as some of transmitted data may include control signals, the data may be transmitted at greater rate than normal absorption capacity of the printer. A local control unit comprises a free running oscillator 11 feeding a frequency dividing counter 13 having a synchronizing reset input 14. The falling edge of a start bit, through AND 15, triggers monostable circuit 16 resetting counter 13 which delivers a pulse M1 = duration of one bit T, after which further pulses M2, M3 are delivered after every 8 counter input pulses. A flip-flop 21 prevents setting of counter 13 by any falling edge following the first. Flip-flop 21 is set by inverted input signal through 10 and may be additionally reset through monostable 16 for duration T in which conditions AND 15 is primed. The timing circuit includes a counter 22 which is reset by a first M3 pulse and stepped on by further M3 pulse through AND 24 when flip-flop 21 is set. A signal DESE is generated when counter 22 has received eight M3 pulses indicating that a start bit and seven information bits have been received and 9th M3 pulse causes reset of flip-flop 21 so that after next M 1 pulse i.e. with coincidence of a stop bit, the next M3 pulse resets counter 22. This sequence is repeated for the next block provided another start bit is received. Receive signals also pass through AND gate 25, Fig. 6, to eight bit register 26 stepped also by M3 pulses when AND 27 is enabled. At the 9th M3 pulse 7 information + 1 parity bit are in register 26 which connects with 8 bit registers 29, 130 and a decoder 28 which recognizes "service" codes i.e. specific operations, e.g. carriage return or whether the peripheral unit is reactivated. Such service codes, by signals generated by flip-flops 33, 40, are transferred into register 130 which determines any operations of incoming data until replaced by the next service code. The asynchronous printer has a variable printing speed due to variation of time needed to position the character head, carriage return &c. and the above arrangement is stated to allow higher transmission rate of characters (including service codes) and actual acceptance rate of binary (printing) characters. Other types of devices, e.g. mosaic printers, magnetic recorders, tape and card punches may be used. Where a peripheral device is located remotely, a lower transmisstion speed may be necessary, or alternatively non-effective padding words may be used to allow for service operations. By juxtaposition of terminal connections (see Fig. 3, not shown) the same interface may be used for both local connection between controller and peripheral device also for remote connection.