UPD6708 datasheet(33/72 Pages) NEC

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µPD6708

5.2.3

MREQ1 command (command code: 0010)

(1)

Functions

This command executes a master communication (transmission or reception). After execution of the command, the unit

begins communication as the master unit. As long as it does not lose in arbitration, the master unit will communicate with

the slave unit which has the slave address specified by SETSA command.

<1> Selected broadcast communication or ordinary communication

Broadcast communication selection

: 0H (broadcast bit ‘0’ output)

Ordinary communication selection

: 8H (broadcast bit ‘1’ output)

<2> Sets the control bits (4 bits)

<3> Sets the number of transmit data bytes (8 bits) (transmission only)

Table 5-6. Number of Transmit Data Bytes Setting

Number of Transmit Data Bytes

Command Parameter

1 byte

2 bytes

255 bytes

FFH

256 bytes

00H

<4> Sets the transmit data (transmission only)

(2)

Example

When the MREQ1 command is used to select ‘ordinary communication’, set the control bit to ‘AH’ (command write and

lock), the number of transmit data bytes to 4, and the transmit data to 12H, 34H, 56H, and 78H, the contents of WDB and

CMR are shown below.

Caution Transmit data 56H and 78H should be set when the above command parameters have been read and WDB

is empty.

1000

1010

0000

0100

0010

First Byte

Second Byte

Broadcast

Bits

Number of Transmit

Data Bytes

Third Byte

Fourth Byte

WDB

CMR

Control

Bits

First

Data Byte

Second

Data Byte

0011

0010

0001

0100

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