Intel mcs-48 manual 8155/8156/8155-2/8156-2, 8155/8156 PIN Functions, Timer OUT

8155/8156/8155-2/8156-2

8155/8156 PIN FUNCTIONS

§ymbol	Function
RESET	Pulse provided by the 8085A to ini-
(input)	tialize the system (connect to 8085A
	RESET OUT). Input high on this line
	resets the chip and initializes the
	three 1/0 ports to input mode. The
	width of RESETpulseshouldtypically
	be two 8085A clock cycle times.
ADo-7	3-state AddresslData lines that inter-
(input)	face with the CPU lower 8-bit Ad-
	dresslData Bus. The 8-bit address is
	latched into the address latch inside
	the 8155156 on the falling edge of
	ALE. The address can be either for
	the memory section or the 1/0 section
	depending on the 10iiVi input. The
	8-bit data is either written into the
	chip or read from the chip, depending
	on the WR or RD input signal.
CE or CE	Chi'pEnable: On the 8155, this pin is
(input)	CE and is ACTIVE LOW. On the 8156,
	this pin is CE and is ACTIVE HIGH.
RD	Read control: Input low on this line
(input)	with the Chip Enable active enables
	and ADo-7 buffers. If 10/iVi pin is low,
	the RAM content will be read out to
	the AD bus. Otherwise the content
	of the selected 1/0 port or commandl
	status registers will be read to the
	AD bus.
WR	Write control: Input low on this line
(input)	with the Chip Enable active causes
	the data on the AddresslData bus to
	be written to the RAM or 1/0 ports and
	commandlstatus register depending
	on 101M.

§y'mbol	Function
ALE	Address Latch Enable: This control
(input)	signal latches both the address on the
	ADo-7 lines and the state of the Chip
	Enable and 101M into the chip at the
	falling edge of ALE.
101M	Selects memory if low and I/O and
(input)	commandlstatus registers if high.
PAO-7(8)	These 8 pins are general purpose 1/0
(input/output)	pins. The inlout direction is selected
	by	programming		the	command
	register.
PBO-7(8)	These 8 pins are general purpose I/O
(input/output)	pins. The inlout direction is selected
	by	programming		the	command
	register.
PCo-5(6)	These 6 pins can function as either
(input/output)	input port, output port, or as control
	signals for PA and PB. Programming
	is done through the command reg-
	ister. When PCO-5 are used as control
	signals, they will provide the fol-
	lowing:
	PCo - A INTR (Port A Interrupt)
	PC1 ~ ABF (Port A Buffer Full)
	PC2 -		A STB (Port A Strobe)
	PC3 - B INTR (Port B Interrupt)
	PC4 - B BF (Port B Buffer Full)
	PC5 -		B STB (Port B Strobe)
TIMER IN	Input to the counter-timer.
(input)
TIMER OUT	Timer output. This output can be
(output)	either a square wave or a pulse de-
	pending on the timer mode.
Vcc	+5 volt supply.
Vss	Ground Reference.

6-83