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CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
(11) IEBus communication success counter (SCR)
The IEBus communication success counter (SCR) indicates the number of remaining communication bytes.
This register reads the count value of the counter in the value set by the IEBus telegraph length register (DLR)
is decremented by ACK in the data field. When the count value has reached “00H”, the communication end flag
(ENDTRNS) of the IEBus interrupt status register (ISR) is set.
Figure 17-26. Format of IEBus Communication Success Counter (SCR)
Note The actual hard counter consists of 9 bits. When “00H” is read, it cannot be judged whether the remaining
number of communication data bytes is 0 (end of communication) or 256.
Therefore, either the
communication end flag is used, or if “00H” is read when the first interrupt occurs at the beginning of
communication, the remaining number of communication data bytes is judged to be 256.
(12) IEBus transmit counter (CCR)
The IEBus transmit counter (CCR) indicates the number of remaining bytes of the communication byte number
specified in the communication mode.
Bits 7 to 0 of the IEBus transmit counter (CCR) indicate the number of transfer bytes.
This register reads the count value of the counter that is preset to the maximum number of transmitted bytes
(32 bytes) per frame specified in mode 1. Whereas SCR (IEBus communication success counter) is decremented
during normal communication (ACK), CCR is decremented when 1 byte has been communicated, regardless of
whether ACK or NACK. When the count value has reached “00H”, the frame end flag (ENDFRAM) of the IEBus
interrupt status register (ISR) is set.
The maximum number of transfer bytes of the preset value of mode 1 per frame is 20H (32 bytes).
Figure 17-27. Format of IEBus Transmit Counter (CCR)
CCR
After reset: 20H
R
Address: FFBFH
1 byte
2 bytes
:
32 bytes
:
255 bytes
0 bytes (end of communication)
or 256 bytesNote
Remaining number of
communication data bytes
Bit
Setting
value
SCR
7
0
:
0
:
1
0
5
0
:
1
:
1
0
3
0
:
0
:
1
0
1
0
1
:
0
:
1
0
6
0
:
0
:
1
0
4
0
:
0
:
1
0
2
0
:
0
:
1
0
1
0
:
0
:
1
0
After reset: 01H
R
Address: FFBEH
01H
02H
:
20H
:
FFH
00H