UPD6708 datasheet(11/72 Pages) NEC

11 / 72 page

µPD6708

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Master address field

The master address field is used to transmit the unit address of the master unit (master address) to the other units.

The master address field consists of master address bits and a parity bit.

The master address comprises 12 bits and is output from the MSB.

If two or more units start transmitting the broadcast bit of the same value simultaneously, the arbitration decision is made

by the master address field.

The master address field compares the data the master has output with the data on the bus each time the master transmits

1 bit of data. If the master address output by the master unit is different from the data on the bus, the master unit assumes

that it has lost in arbitration, stops transmission, and enters the reception state.

Because the IEBus has a wired-AND configuration, the unit having the lowest master address of the units participating

in the arbitration (arbitration masters) wins in the arbitration. Ultimately, only one unit remains in the transmission state

as the master unit after outputting a 12-bit master address.

This master unit then outputs a parity bit Note, makes the other units confirm the master address, and then outputs the

slave address field.

Note

Even parity is used. When the number of the bits that are ‘1’ in the master address is odd, the parity bit is ‘1’.

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Slave address field

The slave address field is used to transmit the address (slave address) of a unit (slave unit) with which the master wishes

to communicate.

The slave address field consists of slave address bits, a parity bit, and an acknowledge bit.

The slave address comprises 12 bits and is output from the MSB. After the 12-bit slave address is transmitted, the parity

bit is output to prevent the slave address from being received incorrectly. Next, the master unit looks for the acknowledge

signal (bit) from the slave unit to confirm that the slave unit exists on the bus. When the master unit detects the acknowledge

signal, it starts outputting the control field. In the case of broadcast communication, however, the master unit outputs the

control field without waiting for the acknowledge bit.

A slave unit outputs the acknowledge signal if it has detected that its slave address coincides with that selected by the

master and that the parities of both the master and slave addresses are even. If the parity is odd, the slave unit assumes

that the master or slave address has not been correctly received, and does not output the acknowledge signal. In this case,

the master unit enters the standby (monitor) state and communication ceases.

In the case of broadcast communication, the slave address is used to distinguish between group broadcast and general

broadcast as follows:

Slave address = FFFH: General broadcast communication

Slave address

≠ FFFH: Group broadcast communication

Remark

In the case of group broadcast communication, the group number is the value of higher 4 bits of the slave

address.

UPD6708 数据表(PDF) 11 Page - NEC

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