4-351

TABLE 1. SUMMARY OF 82C89 MODES, REQUESTING AND RELINQUISHING THE MULTI-MASTER SYSTEM BUS

SINGLE LINES FROM

80C86 OR 80C88 OR 8088

IOB MODE

ONLY

IOB = LOW

RESB = LOW

RESB MODE ONLY

IOB = HIGH, RESB = HIGH

IOB MODE RESB MODE

IOB = LOW, RESB = HIGH

SINGLE BUS

MODE

IOB = HIGH

RESB = LOW

S2

S1

S0

SYSB/RESB =

HIGH

SYSB/RESB =

LOW

SYSB/RESB =

HIGH

SYSB/RESB =

LOW

I/O

Commands

0

0

0

0

0

1

0

1

0

X

X

X

†

†

†

X

X

X

X

X

X

X

X

X

†

†

†

Halt

0

1

1

X

XXXX

X

Memory

Commands

1

1

1

0

0

1

0

1

0†

†

†

†

†

†

†

X

X

X

†

†

†

X

X

X

†

†

†

Idle

1

1

1

X

XXXX

X

NOTES:

1. X = Multi-Master System Bus is allowed to be Surrendered.

2. † = Multi-Master System Bus is Requested.

MODE

PIN

STRAPPING

MULTI-MASTER SYSTEM BUS

REQUESTED**

SURRENDERED*

Single Bus Multi-Master Mode

IOB = High

RESB = Low

Whenever the processor’s status lines

go active

HLT + TI • CBRQ + HPBRQ ‡

RESB Mode Only

IOB = High

RESB = High

SYSB/RESB + High •

ACTIVE STATUS

(SYSB/RESB = Low + TI) •

CBRQ + HLT + HPBRQ

IOB Mode Only

IOB = Low

RESB = Low

Memory Commands

(I/O Status + TI) • CBRQ + HLT +

HPBRQ

IOB Mode RESB Mode

IOB = Low

RESB = High

(Memory Command) •

(SYSB/RESB = High)

(I/O Status Commands) +

SYSB/RESB = Low) • CBRQ +

HPBRQ + HLT

NOTES:

* LOCK prevents surrender of Bus to any other arbiter, CRQLCK prevents surrender of Bus to any lower priority arbiter.

** Except for HALT and Passive or IDLE Status.

‡ HPBRQ, Higher priority Bus request or BPRN = 1.

1. IOB Active Low.

2. RESB Active High.

3. + is read as “OR” and • as “AND”

4. TI = Processor Idle Status S2, S1, S0 = 111

5. HLT = Processor Halt Status S2, S1, S0 = 011

82C89