Motorola MVME2400 Series Programmer's Reference Manual page 147

A value of all zeros will always be returned within the KEY field
during read cycles.
ENAB (ENAB) This field determines whether or not the WDT is
enabled. If a one is written to this bit, the timer will be enabled. A zero
written to this bit will disable the timer. The ENAB bit may only be
modified on the second step of a successful two step arming process.
ARM (ARMED) This read-only bit indicates the armed state of the
register. If this bit is a zero, the register is unarmed. If this bit is a one,
the register is armed for a write.
RES (RESOLUTION) This field determines the resolution of the
timer. The RES field may only be modified on the second step of a
successful two step arming process. The following table shows the
different options associated with this bit.
RES
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
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Timer Resolution Approximate Max Time
1 us
2 us
4 us
8 us
16 us
32 us
64 us
128 us
256 us
512 us
1024 us
2048 us
4096 us
8192 us
16,384 us
32,768 us
Registers
64 msec
128 msec
256 msec
512 msec
1 sec
2 sec
4 sec
8 sec
16 sec
32 sec
1 min
2 min
4 min
8 min
16 min
32 min
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