MC68020 Motorola, MC68020 Datasheet - Page 122

• Manufacturer Part Number: MC68020
• Description: (MC68020 / MC68EC020) MICROPROCESSORS USERS MANUAL
• Manufacturer: Motorola

The existing three-wire arbitration design (BR, BG, and BGACK) of some peripherals can
be converted to the MC68EC020 two-wire arbitration with the addition of an AND gate.
Figure 5-50 shows the combination of BR and BGACK for a three-wire arbitration system
to BR of the MC68EC020 or BR and BG from an MC68EC020 to BG for a three-wire
arbitration system. The speed of the AND gate must be faster than the time between the
assertion of BGACK and the negation of BR by the alternate bus master. Figure 5-50
assumes the alternate bus master does not assume bus mastership until the MC68EC020
AS is negated and MC68EC020 BG is asserted.
MOTOROLA
SIZ1–SIZ0
FC2–FC0
DSACK1
DSACK0
D31–D0
A23–A0
Figure 5-49. MC68EC020 Bus Arbitration Operation Timing—Bus Inactive
CLK
R/W
AS
DS
BR
BG
PROCESSOR
S4
(ARBITRATION PERMITTED
WHILE THE PROCESSOR IS
INACTIVE OR HALTED)
BUS INACTIVE
M68020 USER’S MANUAL
ALTERNATE MASTER
S0
PROCESSOR
5- 75