UPD6708 datasheet(18/72 Pages) NEC

18 / 72 page

µPD6708

(2)

Transferring data command (control bit: read (3H, 7H), write (AH, BH, EH, FH))

During data read (3H, 7H), the data in the data buffer of the slave unit are read to the master unit.

During data write (BH, FH) or during command write (AH, EH), the data the slave unit has received are processed

according to the operation convention.

Remarks

The user can voluntarily select data and command as his system requires.

Control bits 3H, AH, and BH may be locked depending on the communication condition and status.

(3)

Reading lock address (control bits: 4H, 5H)

When the lock address is read processing (4H, 5H), the address (12 bits) of the master unit that has issued the lock

instruction is read in 1-byte units, as shown below.

Figure 2-3. Lock Address Configuration

(4)

Locking and unlocking (locking (3H, AH, BH), unlocking (6H))

The lock function is used to transfer a message over two or more frames.

A locked unit receives data only from the unit that has locked the unit.

Locking and unlocking are performed as described below.

<1> Locking

After the transmission/reception of the acknowledge bit ‘0’ of the message length field by the control bits (3H, AH,

BH) which specify the lock has ended, if the communication frame is completed without completing the transmission or

reception of the number of data bytes specified by the message length bits, the slave unit is locked by the master unit.

At this time, the bit (bit 2) relating to the locking of the byte which indicates the slave status is set to ‘1’.

<2> Unlocking

After completion of transmission or reception of data in one frame by the number of data bytes specified by the message

length bits with control bits (3H, AH, or BH) specifying locking or control bits (6H) specifying unlocking, the slave unit

is unlocked by the master unit. At this time, the bit (bit 2) relating to the locking of the byte which indicates the slave

status is reset to ‘0’.

Locking and unlocking are not performed in the case of broadcast communication.

Caution

To unlock the unit specified to be unlocked by the unit itself, the INIT command (see 5.2.1 “INIT

command”) must be executed with the

µPD6708 (Whether a unit is locked or not can be checked by using

the GETSA command (see 5.2.7 “GETSA command”).

MSB

LSB

Lower 8 Bits

Undefined

Higher 4 Bits

Control Bits : 4H

Control Bits : 5H

UPD6708 数据表(PDF) 18 Page - NEC

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