UPD6708 datasheet(38/72 Pages) NEC

38 / 72 page

µPD6708

RETURN CODES

The

µPD6708 sets the communication status as a return code in lower 4 bits of the status register (STR) and requests

an interrupt (IRQ output). As a result of the interrupt request from the

µPD6708, the host controller can ascertain the

communication result by reading the return code in the status read mode.

6.1

Return Codes in Master/Slave Data Transmission

Table 6-1 shows the return codes placed in the status register when a unit has executed the MREQ1 or MREQ2 command

and becomes the master unit (including broadcast communication), and when the SETSD command is executed and the

slave unit transmits data.

Table 6-1. Return Codes in Master/Slave Transmission

Return Code Name

Code

Description

Transmission start

0000

Indicates that master/slave transmission will start. The point of generation differs

between master transmission and slave transmission.

<1> Master transmission

Set when the master address field ends and the unit wins as the master

unit.

<2> Slave transmission

Set when control bits (3H, 7H) which request data transmission are

received from the master unit.

Transmission normal termination

0010

Indicates that transmission of the number of data bytes specified by the message

length bits has ended within one frame.

Termination during transmission

0011

Indicates that the communication has ended without completion of transmission

of the number of data bytes specified by the message length bits within one frame.

In master transmission, termination during transmission is not flagged if the unit

loses once in arbitration, and transmission is attempted up to three times.

6.2

Return Codes in Master Reception

Table 6-2 shows the return codes placed in STR when a unit has executed the MREQ1 or MREQ2 command and becomes

the master unit, and receives data, a status or lock address from a slave unit.

UPD6708 Datasheet(PDF) 38 Page - NEC