Dmac ton/toff timers, And vmebus global time-out control register -66 – Motorola MVME172 User Manual
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2-66
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VMEchip2
2
DMAC Ton/Toff Timers and VMEbus Global Time-out Control Register
This register controls the DMAC time off timer, the DMAC time on timer,
and the VMEbus global time-out timer.
VGTO
These bits define the VMEbus global time-out value.
When DS0 or DS1 is asserted on the VMEbus, the timer
begins timing. If the timer times out before the data
strobes are removed, a BERR signal is sent to the
VMEbus. The global time-out timer is disabled when the
VMEchip2 is not system controller.
0
8
µ
s
1
64
µ
s
2
256
µ
s
3
The timer is disabled
TIME ON
These bits define the maximum time the DMAC spends
on the VMEbus:
0
16
µ
s
4
256
µ
s
1
32
µ
s
5
512
µ
s
2
64
µ
s
6
1024
µ
s
3
128
µ
s
7
When done (or no data)
TIME OFF
These bits define the minimum time the DMAC spends
off the VMEbus:
0
0
µ
s
4
128
µ
s
1
16
µ
s
5
256
µ
s
2
32
µ
s
6
512
µ
s
3
64
µ
s
7
1024
µ
s
ADR/SIZ
$FFF4004C (8 bits of 32)
BIT
23
22
21
20
19
18
17
16
NAME
TIME OFF
TIME ON
VGTO
OPER
R/W
R/W
R/W
RESET
0 PS
0 PS
0 PS