87C196 datasheet(33/34 Pages) INTEL

33 / 34 page

87C196KT87C196KS

87C196KTKS DESIGN CONSIDERATIONS

1 EPA TIMER RESETWRITE CONFLICT

If the user writes to the EPA timer at the same

time that the timer is reset it is indeterminate

which will take precedence Users should not

write to a timer if using EPA signals to reset it

2 VALID TIME MATCHES

The timer must incrementdecrement to the

compare value for a match to occur A match

does not occur if the timer is loaded with a value

equal to an EPA compare value Matches also do

not occur if a timer is reset and 0 is the EPA

compare value

3 P6

PIN4-7 NOT UPDATED IMMEDIATELY

Values written to P6

REG are temporarily held

in a buffer If P6

MODE is cleared the buffer is

loaded into P6

REGx If P6

MODE is set the

value stays in the buffer and is loaded into

REGx when P6

MODEx is cleared Since

reading P6

REG returns the current value in

REG and not the buffer

changes to

REG

cannot

read

untilunless

MODEx is cleared

4 WRITE CYCLE DURING RESET

If RESET occurs during a write cycle the con-

tents of the external memory device may be cor-

rupted

5 INDIRECT SHIFT INSTRUCTION

The upper 3 bits of the byte register holding the

shift count are not masked completely If the shift

count register has the value 32 c n where

n e 1 3 5 or 7 the operand will be shifted 32

times This should have resulted in no shift taking

place

6 PORT 4 ADDRESS BEHAVIOR

For bus timing Modes 1 and 2 specified only on

the 87C196KTKS C-step Port 4 does not retain

the address during the data portion of the bus

cycle

Designs using an 8-bit external memory

system in bus Mode 1 or Mode 2 require an ex-

ternal latch on Port 4 to retain the address during

the data portion of the bus cycle Designs using

an 8-bit external memory system in the KR or

KR a 1 Wait

bus timing modes do not require an

external latch

Designs using 16-bit external

memory systems require an external latch on

both Port 3 and Port 4 in all bus timing modes

87C196 Datasheet(PDF) 33 Page - Intel Corporation

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