UPD6708 datasheet(44/72 Pages) NEC

44 / 72 page

µPD6708

7.1.2

Master transmission by MREQ2 command

If the MREQ1 command is executed and a communication error occurs during the transmission of data or a command,

with the result that not all the data is transmitted, the remaining data can be transmitted by executing the MREQ2 command.

(1)

The remaining data is placed in WDB as command parameters as shown in Figure 7-2, and the MREQ2 command

(command code: 3H) is executed.

Figure 7-2. Data Exchange During Master Transmission (Contents of Write Data Buffer)

Transmit Data (N-th Byte)

First Byte

Second Byte

Third Byte

Fourth Byte

WDB

Transmit Data (Byte N+2)

Transmit Data (Byte N+3)

Transmit Data (Byte N+1)

The remaining operations are the same as 7.1.1 “Master transmission by MREQ1 command”.

7.2

Slave Transmission

7.2.1

Data transmission

When the slave unit receives control bit 3H or 7H from the master unit, it transmits data as follows.

(1)

It places the number of transmit data bytes and transmit data in WDB as command parameters as shown in Figure

7-3, and executes the SETSD command (command code: 5H).

(2)

When the unit receives control bit 3H or 7H from the master unit, the “transmission start” return code (0H) is placed

in STR, and an interrupt request is generated. At this time, the host controller places the fourth and following bytes of

transmit data in WDB.

Figure 7-3. Data Exchange During Slave Transmission (Contents of WDB)

First Byte

Second Byte

Third Byte

Fourth Byte

WDB

Transmit Data (Second Byte) Transmit Data (Third Byte)

Number of Transmit

Data Bytes

Transmit Data (First Byte)

(3)

If the number of data or command bytes specified by “number of transmit data bytes” is transmitted correctly, a

“transmission end” return code (2H) will be placed in STR and an interrupt request will be generated.

(4)

If an error occurs during transmission and the data communication is halted, a “termination during transmission” return

code (3H) will be placed in STR and an interrupt request will be generated.

The timing at which the

µPD6708 reads transmit data from WDB is shown below.

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