4

Pin Descriptions

SYMBOL

PIN

NUMBER

TYPE

DESCRIPTION

The following pin function descriptions are for HS-80C86RH systems in either minimum or maximum mode. The “Local Bus” in these descriptions

is the direct multiplexed bus interface connection to the HS-80C86RH (without regard to additional bus buffers).

AD15-AD0

2-16, 39

I/O

ADDRESS DATA BUS: These lines constitute the time multiplexed memory/IO address (T1) and data

(T2, T3, TW, T4) bus. AO is analogous to BHE for the lower byte of the data bus, pins D7-D0. It is LOW

during T1 when a byte is to be transferred on the lower portion of the bus in memory or I/O operations.

Eight-bit oriented devices tied to the lower half would normally use AD0 to condition chip select functions

(See BHE). These lines are active HIGH and are held at high impedance to the last valid logic level during

interrupt acknowledge and local bus “hold acknowledge” or “grant sequence”.

A19/S6

A18/S5

A17/S4

A16/S3

35-38

O

ADDRESS/STATUS: During T1, these are the four most significant address lines for memory operations.

During I/O operations these lines are low. During memory and I/O operations, status information is

available on these lines during T2, T3, TW, T4. S6 is always zero. The status of the interrupt enable FLAG

bit (S5) is updated at the beginning of each CLK cycle. S4 and S3 are encoded.

This information indicates which segment register is presently being used for data accessing. These lines

are held at high impedance to the last valid logic level during local bus “hold acknowledge” or “grant

sequence”.

S4

S3

0

0

Extra Data

0

1

Stack

1

0

Code or None

1

1

Data

BHE/S7

34

O

BUS HIGH ENABLE/STATUS: During T1 the bus high enable signal (BHE) should be used to enable data

onto the most significant half of the data bus, pins D15-D8. Eight bit oriented devices tied to the upper

half of the bus would normally use BHE to condition chip select functions. BHE is LOW during T1 for read,

write, and interrupt acknowledge cycles when a byte is to be transferred on the high portion of the bus.

The S7 status information is available during T2, T3 and T4. The signal is active LOW, and is held at high

impedance to the last valid logic level during interrupt acknowledge and local bus “hold acknowledge” or

“grant sequence”; it is LOW during T1 for the first interrupt acknowledge cycle.

BHE

A0

0

0

Whole Word

0

1

Upper Byte from/to Odd Address

1

0

Lower Byte from/to Even Address

1

1

None

RD

32

O

READ: Read strobe indicates that the processor is performing a memory or I/O read cycle, depending

on the state of the M/IO or S2 pin. This signal is used to read devices which reside on the HS-80C86RH

local bus. RD is active LOW during T2, T3 and TW of any read cycle, and is guaranteed to remain HIGH

in T2 until the 80C86 local bus has floated.

This line is held at a high impedance logic one state during “hold acknowledge” or “grant sequence”.

READY

22

I

READY: is the acknowledgment from the addressed memory or I/O device that will complete the data

transfer. The RDY signal from memory or I/O is synchronized by the HS-82C85RH Clock Generator to

form READY. This signal is active HIGH. The HS-80C86RH READY input is not synchronized. Correct

operation is not guaranteed if the Setup and Hold Times are not met.

INTR

18

I

INTERRUPT REQUEST: is a level triggered input which is sampled during the last clock cycle of each

instruction to determine if the processor should enter into an interrupt acknowledge operation. If so, an

interrupt service routine is called via an interrupt vector lookup table located in system memory. INTR is

internally synchronized and can be internally masked by software resetting the interrupt enable bit. This

signal is active HIGH.

TEST

23

I

TEST: input is examined by the “Wait” instruction. If the TEST input is LOW execution continues,

otherwise the processor waits in an “Idle” state. This input is synchronized internally during each clock

cycle on the leading edge of CLK.

HS-80C86RH