UPD784938 Datasheet, PDF (490/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
(6) Telegraph length register (DLR)
[During transmission unit] ... Master transmission, slave transmission
The data of this register is reflected on 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.
[During reception unit] ... Master reception, slave reception
The receive data in the telegraph length field transmitted from the transmission unit is written to this register.
Figure 20-20. Telegraph Length Register (DLR) Format
7
6
5
4
3
2
1
0 Address After reset R/W
DLR 0
0
0
0
0
0
0
0 0FFB9H 01H R/W
Remaining Number of
Communication Data Bytes
01H
1 byte
02H
2 bytes
20H
32 bytes
FFH
255 bytes
00H
256 bytes
Cautions 1. If the master issues a request “0H, 4H, 5H, or 6H” to transmit a slave status and lock address
(high-order 4 bits, low-order 8 bits), the contents of this register are set to “01H” by hardware;
therefore, the CPU does not have to set this register.
An instruction of Read Modify Write mode (such as XCH and ROL4) cannot be used for DLR.
2. In the case of defeat in a bus conflict and a slave status request is received from the unit that
won, DLR is fixed to “01H”. Therefore, if a re-request of the master follows, the appointed
telegraph length must be set to DLR.
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Preliminary User’s Manual U13987EJ1V0UM00