
MOTOROLA
M68000 8-/16-/32-BIT MICROPROCESSORS USER'S MANUAL
10-17
10.12 AC ELECTRICAL SPECIFICATIONS — BUS ARBITRATION 
(VCC=5.0
VDC
±
5%; GND=0 VDC, TA=TL TO TH; See Figure s 10-7 – 10-11) (Applies To All Processors
Except The MC68EC000)
Num
Characteristic
8 MHz*
10 MHz*
12.5 MHz*
16.67 MHz
12F
16 MHz
20 MHz
Unit
Min
Max
Min
Max
Min
Max
Min
Max
Min
Max
Min
Max
7
Clock High to Address, Data
Bus High Impedance
(Maximum)
—
80
—
70
—
60
—
50
—
50
—
42
ns
16
Clock High to Control Bus
High Impedance
—
80
—
70
—
60
—
50
—
50
—
42
ns
33
Clock High to 
BG
 Asserted
—
62
—
50
—
40
0
40
0
30
0
25
ns
34
Clock High to 
BG
 Negated
—
62
—
50
—
40
0
40
0
30
0
25
ns
35
361
BR
 Asserted to 
BG
 Asserted
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
Clks
BR
 Negated to 
BG
 Negated
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
Clks
37
BGACK
 Asserted to 
BG
Negated
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
1.5
3.5
Clks
37A2
BGACK
 Asserted to 
BR
Negated
20
1.5
Clks
20
1.5
Clks
20
1.5
Clks
10
1.5
Clks
10
1.5
Clks
10
1.5
Clks
Clks/
ns
38
BG
 Asserted to Control,
Address, Data Bus High
Impedance (
AS
 Negated)
80
70
60
—
50
—
50
—
42
ns
39
BG
Width Negated
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
Clks
46
BGACK
 Width Low
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
Clks
47
Asynchronous Input Setup
Time
10
—
10
—
10
—
5
—
5
—
5
—
ns
57
BGACK
 Negated to 
AS, DS
,
R/
W
 Driven
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
Clks
57A
BGACK
 Negated to FC, 
VMA
Driven
1
—
1
—
1
—
1
—
1
—
1
—
Clks
581
BR
 Negated to 
AS
, 
DS
, R/
W
Driven
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
1.5
—
Clks
58A1
BR
 Negated to FC, 
VMA
Driven
1
—
1
—
1
—
1
—
1
—
1
—
Clks
*These specifications represent improvement over previously published specifications for the 8-, 10-, and 12.5-MHz
MC68000 and are valid only for product bearing date codes of 8827 and later.
** Applies only to the MC68HC000 and MC68HC001.
NOTES:
1. Setup time for the synchronous inputs 
BGACK
, 
IPL0
-
IPL2
 , and 
VPA
  guarantees their recognition at the 
next falling edge of the clock.
2.
 BR
 need fall at this time only in order to insure being recognized at the end of the bus cycle.
3. Timing measurements are referenced to and from a low voltage of 0.8 volt and a high voltage of 2.0 volts, 
unless otherwise noted. The voltage swing through this range should start outside and pass through the 
range such that the rise or fall will be lienar between 0.8 volt and 2.0 volts.
4. The processor will negate 
BG
 and begin driving the bus again if external arbitration logic negates 
BR
 before 
asserting 
BGACK
.
5. The minimum value must be met to guarantee proper operation. If the maximum value is exceeded, 
BG
 may
be reasserted.