UPD6708 datasheet(17/72 Pages) NEC

17 / 72 page

µPD6708

(1)

Reading slave status (SSR) (control bit: 0H, 6H)

The master unit can learn the reason why the slave unit has not returned the acknowledge bit (ACK) by reading the

slave status.

The slave status is determined by the results of the last communication performed by the slave unit.

All the slave units can provide slave status information.

The meanings of the slave status are shown in Table 2-5.

Figure 2-2. Bit Configuration of Slave Status (SSR)

Table 2-5. Meanings of Slave Status

Bit

Value

Meaning

Bit 0 Note 1

Slave transmit buffer empty

Slave transmit buffer is not empty.

Bit 1 Note 2

Slave receive buffer empty

Slave receive buffer is not empty.

Bit 2

Unit is not locked.

Unit is locked.

Bit 3

Fixed to ‘0’

Bit 4 Note 3

Slave transmission ends

Slave transmission enabled

Bit 5

Fixed to ‘0’

Bit 7

Mode 0

Indicates the highest mode the unit

Bit 6

Mode 1

supports Note 4.

Mode 2

For future expansion

Notes 1.

The slave transmit buffer is the buffer accessed during data read processing (control bits: 3H, 7H).

With the

µPD6708, this buffer corresponds to the write data buffer (WDB) when the SETSD command is valid

(see 5.2.6 “SETSD command”).

The slave receive buffer is the buffer accessed during data write processing (control bits: 8H, AH, BH, EH, FH).

With the

µPD6708, this buffer corresponds to the read data buffer (RDB).

The value of bit 4 can be selected by INIT command (see 5.2.1 “INIT command”).

Because the

µPD6708 can support mode 2, bits 7 and 6 are fixed at ‘10’.

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

MSB

LSB

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