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CHAPTER 17
IEBus CONTROLLER (
PD178096A, 178098A, 178F098 ONLY)
User’s Manual U12790EJ2V0UD
(6) IEBus telegraph length register (DLR)
(a) Transmission unit (master transmission, slave transmission)
The data of this register is reflected in the data transmitted in the telegraph length field and indicates the
number of bytes of the transmit data. This register must be set in advance before transmission.
(b) Reception unit (master reception, slave reception)
The receive data in the telegraph length field transmitted from the transmission unit is written to this register.
Remark
The IEBus telegraph length register consists of a write register and a read register. Consequently,
data written to this register cannot be read as is. The data that can be read is the data received
during IEBus communication.
Figure 17-20. Format of IEBus Telegraph Length Register (DLR)
Cautions 1. If the master issues a request “0H, 4H, 5H, or 6H” to transmit a slave status and lock
address (higher 4 bits, lower 8 bits), the contents of this register are set to “01H” by
hardware; therefore, the CPU does not have to set this register.
2. In the case of defeat in a bus conflict and a slave status request is received from the
unit that won, the IEBus telegraph length register (DLR) is fixed to “01H”. Therefore,
when a re-request of the master follows, the appointed telegraph length must be set
to DLR.
3. Instructions in Read Modify Write mode (such as XCH and ROL4) cannot be used for
DLR.
1 byte
2 bytes
:
32 bytes
:
255 bytes
256 bytes
Number of communication
data bytes
Bit
Setting
value
01H
02H
:
20H
:
FFH
00H
DLR
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/W
Address: FFB9H