Intel mcs-48 manual 8291

8291

PIN DESCRIPTION

Symbol	I/O	Pin No.	Function
Do-D7	I/O	12-19	Data bus port, to be connected
			to microprocessor data bus.
RSo-RS2		21-23	Register select inputs, to be con-
			nected to three non-multiplexed
			microprocessor address bus
			lines. Select which of the 8 in-
			ternal read (write) registers will
			be read from (written into) with
			the execution of RD (WR).
		8	Chip select. When low, enables
			reading from or writing into the
			register selected by RSo-RS2.
		9	Read strobe. When low, selected
			register contents are read by the
			CPU.

Symbol	I/O	Pin No.	Function
NRFD	I/O	37	Not ready for data; GPIB hand-
			shake control line. Indicates the
			condition of readiness of de-
			vicels) connected to the bus to
			accept data.
	I/O	38	Not data accepted; GPIB hand-
			shake control line. Indicates the
			condition of acceptance of data
			by the device(s) connected to
			the bus.
		26	Attention; GPIB command line.
			Specifies how data on DIO lines
			are to be interpreted.
		24	Interface clear; GPIB command
			line. Places the interface func-
			tions in a known quiescent state.

10

o 11

DREQ o 6

DACK7

TRIG 0 5

Write strobe. When low, data is written into the selected register.

Interrupt request to the micro- processor, set high for request and cleared when the appropri- ate register is accessed by the CPU. May be software config- ured to be active low.

DMA request, normally low, set high to indicate byte output or byte input, in DMA mode; reset by DACK.

DMA acknowledge. When low, resets DREQ and selects data in/data out register for DMA data transfer (actual transfer done by RD/WR pulse).

Must be high if DMA is not used.

Trigger output, normally low; generates a triggering pulse with 1!,sec min. width in response to the GET bus command or Trigger auxiliary command.

	o	27	Service request; GPIB command
			line. Indicates the need for
			attention and requests an inter-
			ruption of the current sequence
			of events on the GPIB.
		25	Remote enable; GPIB command
			line. Selects (in conjunction with
			other messages I remote or local
			control of the device.
	I/O	39	End or identify; GPIB command
			line. Indicates the end of a
			multiple byte transfer sequence
			or, in conjunction with ATN,
			addresses the device during a
			polling sequence.
T/R1	o		External transceivers control
			line. Set high to indicate output
			data/signals on the D101-D108
			and DAV lines and input signals
			on the NRFD and NDAC lines
			(active source handshake I. Set
			low to indicate input data/
			signals on the D101·D108 and

CLOCK3

RESET4

I/O 36

External clock input, used only for T 1 delay generator. May be any speed in 1-8 MHz range.

Reset input. When high, forces the device into an "Idle" (initiali- zation) mode. The device will re- main at "Idle" until released by the microprocessor.

8-bit GPIB data port, used for bidirectional data byte transfer between 8291 and GPIB via non- inverting external line trans-

ceivers.

Data valid; GPIB handshake control line. Indicates the avail- ability and validity of infor- mation on the DIO lines.

			DAV lines and output signals on
			the NRFD and NDAC lines (ac-
			tive acceptor handshake I.
T/R2	o	2	External transceivers control
			line. Set high to indicate output
			signals on the EOI line. Set low
			to indicate expected input signal
			on the EOI line during parallel
			poll.
Vee	P.S.	40	Positive power supply (5V ±
			10%).
GND	P.S.	20	Potential ground circuit.

Note: All signals on the 8291 pins are specified with positive logic. However, IEEE 488 specifies negative l~ on its 16 signal lines. Thus, the data is inverted once from 00-07 to 0101-0108 and non-inverting bus transceivers should be used.

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