UPD6708 datasheet(13/72 Pages) NEC

13 / 72 page

µPD6708

<2> When master receives data

The message length bits and parity bit are output by the slave unit. The master unit outputs the acknowledge signal

if it detects that the parity bit is even.

If the parity is odd, the master unit assumes that the message length bits have not been received correctly, and returns

to the standby state without outputting the acknowledge signal. In this case, the slave unit also returns to the standby

state, and communication ceases.

(6)

Data field

The data field is used to transmit/receive data to/from the slave units.

The master unit uses the data field to transmit data to and receive data from the slave units.

The data field consists of 8 data bits, a parity bit, and an acknowledge bit.

The data bits are output from the MSB.

Following the data bits, the parity bit and acknowledge bit are output from the master unit and the slave unit, respectively.

Broadcast communication is performed when only the master unit transmits data. At this time, the acknowledge signal

is ignored.

The operation differs depending on whether the master performs transmission or reception, as follows.

<1> When master transmits data

When the master unit writes data to the slave unit, the master unit transmits data bits and a parity bit to the slave unit.

The slave unit receives the data bits and parity bit. If the parity is even and the receive buffer is empty, the slave unit

outputs the acknowledge signal.

If the parity is odd and the receive buffer is not empty, the slave unit denies

acknowledgment of the corresponding data and does not output the acknowledge signal.

If no acknowledge signal is output from the slave unit, the master unit transmits the same data again. The master

unit continues this operation until it detects the acknowledge signal from the slave unit or the data reaches the maximum

number of transfer bytes.

If the parity is even and the acknowledge signal has been output from the slave unit, and if the master unit has more

data to transmit and the maximum number of transfer bytes is not exceeded, the master unit will transmit the next data.

In the case of broadcast communication, the slave unit does not output the acknowledge signal, and the master unit

transfers data on a byte-by-byte basis.

<2> When master receives data

When the master unit reads data from the slave unit, the master unit outputs synchronization signals corresponding

to all the read bits.

The slave unit outputs the contents of the data and parity bits onto the bus in accordance with the synchronization

signals from the master unit.

The master unit reads the data and parity bit output by the slave unit, and checks the parity.

If the parity is odd or the receive buffer is not empty, the master unit denies acknowledgement of that data and does

not output the acknowledge signal. If the data is within the maximum number of transfer bytes that can be transmitted

in one frame, the master unit repeatedly reads the same data.

If the parity is even and the receive buffer is empty, the master unit acknowledges the data and transmits back the

acknowledge signal. If the data is within the maximum number of bytes that can be transmitted in one frame, the master

unit reads the next data.

UPD6708 数据表(PDF) 13 Page - NEC

UPD6708 数据表(HTML) 13 Page - NEC

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