87C196 datasheet(4/34 Pages) INTEL

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87C196KT87C196KS

PIN DESCRIPTIONS

Symbol

Name and Function

VCC

Main supply voltage (a5V)

VSS VSSI VSSI

Digital circuit ground (0V) There are three VSS pins all of which MUST be connected

VREF

Reference for the AD converter (a5V) VREF is also the supply voltage to the analog

portion of the AD converter and the logic used to read Port 0 Must be connected for

AD and Port 0 to function

VPP

Programming voltage for the EPROM parts It should be a125V for programming It

is also the timing pin for the return from powerdown circuit Connect this pin with a

1 mF capacitor to VSS anda1MX resistor to VCC If this function is not used VPP

may be tied to VCC

ANGND

Reference ground for the AD converter Must be held at nominally the same

potential as VSS

XTAL1

Input of the oscillator inverter and the internal clock generator

XTAL2

Output of the oscillator inverter

P27CLKOUT

Output of the internal clock generator The frequency is

the oscillator frequency It

has a 50% duty cycle Also LSIO pin

RESET

Reset input to the chip Input low for at least 16 state times will reset the chip The

subsequent low to high transition resynchronizes CLKOUT and commences a 10-

state time sequence in which the PSW is cleared bytes are read from 2018H and

201AH loading the CCBs and a jump to location 2080H is executed Input high for

normal operation RESET has an internal pullup

P57BUSWIDTH

Input for bus width selection If CCR bit 1 is a one and CCR1 bit 2 is a one this pin

dyamically controls the Buswidth of the bus cycle in progress If BUSWIDTH is low an

8-bit cycle occurs if BUSWIDTH is high a 16-bit cycle occurs If CCR bit 1 is ‘‘0’’ and

CCR1 bit 2 is ‘‘1’’ all bus cycles are 8-bit if CCR bit 1 is ‘‘1’’ and CCR1 bit 2 is ‘‘0’’ all

bus cycles are 16-bit CCR bit 1 e ‘‘0’’ and CCR1 bit 2 e ‘‘0’’ is illegal Also an LSIO

pin when not used as BUSWIDTH

NMI

A positive transition causes a non maskable interrupt vector through memory location

203EH

P51INST

Output high during an external memory read indicates the read is an instruction fetch

INST is valid throughout the bus cycle INST is active only during external memory

fetches during internal EPROM fetches INST is held low Also LSIO when not INST

Input for memory select (External Access) EA equal to a high causes memory

accesses to locations 2000H through 9FFFH to be directed to on-chip EPROMROM

EA equal to a low causes accesses to these locations to be directed to off-chip

memory EA ea125V causes execution to begin in the Programming Mode EA is

latched at reset

P50ALEADV

Address Latch Enable or Address Valid output as selected by CCR Both pin options

provide a latch to demultiplex the address from the addressdata bus When the pin is

ADV it goes inactive (high) at the end of the bus cycle ADV can be used as a chip

select for external memory ALEADV is active only during external memory

accesses Also LSIO when not used as ALE

P53RD

Read signal output to external memory RD is active only during external memory

reads or LSIO when not used as RD

P52WR WRL

Write and Write Low output to external memory as selected by the CCR WR will go

low for every external write while WRL will go low only for external writes where an

even byte is being written WR WRL is active during external memory writes Also an

LSIO pin when not used as WR WRL

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