UPD72042 datasheet(13/92 Pages) NEC

13 / 92 page

µPD72042

Data Sheet S14870EJ1V0DS00

(2) Master address field

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

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

A master address consists of 12 bits. It is output starting with the MSB.

When more than one unit starts transmitting the same broadcast bit value at the same time, arbitration

determination is performed by the master address field.

Each time a unit transmits one bit of the master address field, the unit compares its output data with the data

on the bus. If the comparison indicates that the master address output by the unit differs from the data on the

bus, the unit determines that it has lost an arbitration. The unit stops transmission, and readies itself for reception.

The IEBus is organized by wired AND. When arbitration is performed between units (arbitration masters), the

unit having the smallest master address value wins the arbitration.

After the 12-bit master address has been output, only one unit is finally determined as being the master unit,

such that that unit remains in the transmission state.

Next, the master unit outputs a parity bitNote to post the master address to other units. Then, the master unit

proceeds to the slave address field.

Note

Even parity is used. When the number of 1’s in the master address bits is odd, the parity bit is set to 1.

(3) Slave address field

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

unit wants to communicate.

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

A slave address consists of 12 bits. It is output starting with the MSB. After a 12-bit slave address has been

transmitted, a parity bit is output to prevent the slave address from being received incorrectly. Then, the master

unit attempts to detect the acknowledge signal from a slave unit to confirm that the slave unit exists on the bus.

When the acknowledge signal is detected, the master unit outputs a control field. Note, however, that when

performing broadcast, the master unit outputs the control field without attempting to detect the acknowledge bit.

The slave unit outputs an acknowledge signal when the slave unit recognizes a match between the slave unit’s

address and the slave address transmitted by the master unit match, and that both the master address and slave

address have even parity. If the slave unit detects odd parity, it does not recognize the addresses as matching,

so does not output an acknowledge signal. In this case, the master unit is placed in the standby (monitor) state,

and communication terminates.

For broadcast, the slave address is used to distinguish between group broadcast or general broadcast, as follows:

When the slave address is FFFH

General broadcast

When the slave address is other than FFFH

Group broadcast

Remark For group broadcast, the number of a target group is indicated by the high-order 4 bits of the slave

address.

UPD72042 Datasheet(PDF) 13 Page - NEC