B-61813E/03 CONNECTIONS 8. HIGH SPEED COUNTER MODULE
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8.8.4 Reading data
The CNTS and STTS are two of the four input bytes. The most
significant bit, TRA, of the CNTS and the most significant bit, TRB, of
the STTS can be used to determine whether the count data is correct. If
both TRA and TRB are 0 or 1, the count data is correct.
In almost all cases, both TRA and TRB will be 0 or 1 when you view
the diagnostic display. (Do not determine that the data has not changed
because of the fact that the TRA and TRB do not become 0 or 1
alternately.) Note that the count data does not take a negative
value.
(CNTS)
TRA Counter H
(STTS)
TRB ALM CSP ME MH CMPC CMPB CMPA
TRA TRB Validity
0 0 Correct
0 1 Incorrect
1 0 Incorrect
1 1 Correct
The counter assumes the following data when it is incremented or
decremented.
0000000 00000000 00000010
0000000 00000000 00000001
0000000 00000000 00000000
1111111 11111111 11111111
to
0000000 00000000 00000011
0000000 00000000 00000010
0000000 00000000 00000001
0000000 00000000 00000000
1111111 11111111 11111111
1111111 11111111 11111110
1111111 11111111 11111101
1111111 11111111 11111100
The square represents the TRA. (The most significant bit is the TRA.
It is not a sign bit.)
Increment
Decrement