80C88_08 Datasheet, PDF (5/38 Pages) Intersil Corporation – CMOS 8-/16-Bit Microprocessor

80C88
Pin Description
The following pin function descriptions are for 80C88 system in minimum mode (i.e., MN/MX = V_CC). Only the pin functions which
are unique to the minimum mode are described; all other pin functions are as described above.
SYMBOL
PIN
NUMBER
TYPE
DESCRIPTION
MINIMUM MODE SYSTEM (i.e., MN/MX = V_CC)
IO/M
28
O STATUS LINE: is an inverted maximum mode S2. It is used to distinguish a memory access from an I/O
access. IO/M becomes valid in the T4 preceding a bus cycle and remains valid until the final T4 of the cycle
(I/O = HIGH, M = LOW). IO/M is held to a high impedance logic one during local bus “hold acknowledge”.
WR
29
O Write: strobe indicates that the processor is performing a write memory or write I/O cycle, depending on
the state of the IO/M signal. WR is active for T2, T3, and Tw of any write cycle. It is active LOW, and is held
to high impedance logic one during local bus “hold acknowledge”.
INTA
24
O INTA: is used as a read strobe for interrupt acknowledge cycles. It is active LOW during T2, T3 and Tw of
each interrupt acknowledge cycle. Note that INTA is never floated.
ALE
25
O ADDRESS LATCH ENABLE: is provided by the processor to latch the address into the 82C82/82C83
address latch. It is a HIGH pulse active during clock low of T1 of any bus cycle. Note that ALE is never
floated.
DT/R
27
O DATA TRANSMIT/RECEIVE: is needed in a minimum system that desires to use an 82C86/82C87 data
bus transceiver. It is used to control the direction of data flow through the transceiver. Logically, DT/R is
equivalent to S1 in the maximum mode, and its timing is the same as for IO/M (T = HIGH, R = LOW). This
signal is held to a high impedance logic one during local bus “hold acknowledge”.
DEN
26
O DATA ENABLE: is provided as an output enable for the 82C86/82C87 in a minimum system which uses
the transceiver. DEN is active LOW during each memory and I/O access, and for INTA cycles. For a read
or INTA cycle, it is active from the middle of T2 until the middle of T4, while for a write cycle, it is active from
the beginning of T2 until the middle of T4. DEN is held to high impedance logic one during local bus “hold
acknowledge”.
HOLD,
31
HLDA
30
I
HOLD: indicates that another master is requesting a local bus “hold”. To be acknowledged, HOLD must be
O active HIGH. The processor receiving the “hold” request will issue HLDA (HIGH) as an acknowledgment,
in the middle of a T4 or T1 clock cycle. Simultaneous with the issuance of HLDA the processor will float the
local bus and control lines. After HOLD is detected as being LOW, the processor lowers HLDA, and when
the processor needs to run another cycle, it will again drive the local bus and control lines.
Hold is not an asynchronous input. External synchronization should be provided if the system cannot
otherwise guarantee the set up time.
SS0
34
O STATUS LINE: is logically equivalent to S0 in
the maximum mode. The combination of SS0,
IO/M DT/R SS0 CHARACTERISTICS
IO/M and DT/R allows the system to completely
1
decode the current bus cycle status. SS0 is held
to high impedance logic one during local bus
1
0
0 Interrupt Acknowledge
0
1 Read I/O Port
“hold acknowledge”.
1
1
0 Write I/O Port
1
1
1 Halt
0
0
0 Code Access
0
0
1 Read Memory
0
1
0 Write Memory
0
1
1 Passive
5
FN2949.4
February 22, 2008