Intel mcs-48 manual 108048/8748/8035L

108048/8748/8035L

PIN DESCRIPTION

Designation

VSS

Voo

Vee

PROG

P10·P17

Port 1

P20-P27

Port 2

DBo-DB7

BUS

TO

T1

INT

Pin # Function

20 Circuit GND potential

26Programming power supply; +25V during program, +5V during oper· ation for both ROM and PROM. low power standby pin in 8048 and 8035l.

40Main power supply; +5V during operation and programming.

25Program pulse (+23V) input pin during 8748 programming.

Output strobe for 8243 I/O expander.

27·34 8-bit quasi-bidirectional port.

21-24 8-bit quasi-bidirectional port.

35-38P20-P23 contain the four high order program counter bits during an external program memory fetch and serve as a 4-bit I/O expander bus for 8243.

12-19 True bidirectional port which can be written or read synchronously using the RD, WR strobes. The port can also be statically latched.

Contains the 8 low order program counter bits during an external program memory fetch, and receives the addressed instruction under the control of P5EN. Also contains the address and data during an external RAM data store instruction, under control of ALE, RD, and WR.

Input pin testable using the con- ditional transfer instructions JTO and JNTO. TO can be designated as a clock output using ENTO ClK instruction. TO is also used during programming.

39Input pin testable using the JT1, and JNT1 instructions. Can be des- ignated the timer/counter input using the STRT CNT instruction.

6Interrupt input. Initiates an inter- rupt if interrupt is enabled. Inter- rupt is disabled after a reset. Also testable with conditional jump instruction. (Active low)

Designation	Pin #	Function
RD	8	Output strobe activated during a
		BUS read. Can be used to enable
		data onto the bus from an external
		device.
		Used as a read strobe to external
		data memory. (Active low)
RESET	4	Input which is used to initialize the
		processor. Also used during PROM
		programming verification, and
		power down. (Active low)
		(Non TTL VIH )
WR	10	Output strobe during a bus write.
		(Active low)
		Used as write ·strobe to external
		data memory.
ALE	11	Address latch enable. This signal
		occurs once during each cycle and
		is useful as a clock output.
		The negative edge of ALE strobes
		address into external data and pro-
		gram memory.
PSEN	9	Program store enable. This output
		occurs only during a fetch to exter-
		nal program memory. (Active low)

555 Single step input can be used in con- junction with ALE to "single step" the processor through each in- struction. (Active low)

EA	7	External access input which forces
		all program memory fetches to re-
		ference external memory, Useful
		for emulation and debug, and
		essential for testing and program
		verification. (Active high)
XTAL1	2	One side of crystal input for inter-
		nal oscillator. Also input for exter-
		nal source. (Non TTL VIH)
XTAl2	3	Other side of crystal input.

6-19