UPD6708 datasheet(43/72 Pages) NEC

43 / 72 page

µPD6708

COMMUNICATING WITH HOST CONTROLLER

This section explains the flow of data between the

µPD6708 and the host controller via the serial interface (SCK, SO,

SI pins) during communications.

7.1

Master Transmission

Master transmission is the communication data exchange which takes place when a unit becomes a master unit by

specifying AH, BH, and FH as control bits and executing the MREQ1 or MREQ2 command, and then transmitting data and

commands to slave units.

7.1.1

Master transmission by MREQ1 command

(1)

The control bits, number of transmit data bytes and transmit data are placed in the write WDB as command parameters

as shown in Figure 7-1, and the MREQ1 command (command code: 2H) is executed.

(2)

When a unit wins in arbitration as the master unit (the end of the master address field), the transmission start return

code (0H) is placed in the status register (STR), and an interrupt request is generated for the host controller. At this time,

the host controller places the third and following bytes of transmit data in WDB.

Figure 7-1. Data Exchange During Master Transmission (Contents of WDB)

(3)

If the number of data or command bytes specified by “number of transmit data bytes” are 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.

Table 7-1. Timing for Reading Transmit Data from WDB

(The minimum time after transmission start return code (0H) is set in STR)

Transmit Data

Timing for Reading Transmit Data from WDB (

µs)

Mode 0

Mode 1

Mode 2

Transmit data (first byte)

Approx. 4745

Approx. 1205

Approx. 870

Transmit data (second byte)

Approx. 6325

Approx. 1605

Approx. 1160

Transmit data (N-th byte)

Approx. 3165+1580

× N

Approx. 805+400

× N

Approx. 580+290

× N

Broadcast

Bits

Control Bits

Number of Transmit

Data Bytes

First Byte

Second Byte

Third Byte

Fourth Byte

WDB

Transmit Data (First Byte) Transmit Data (Second Byte)

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