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Bus Description
The interface signal lines are organized into three functional groups:
- Data lines (8 lines)
- Handshake lines (3 lines)
- General bus management lines (5 lines)
The bus signal lines use low true logic protocol.
Data lines:
- allow transfer of one byte at a time.
- Bytes are transferred over the interface in a byte-serial, bit-parallel
manner.
- DIO1 represents least significant bit of the byte, while DIO8 represent
most significant bit of the byte transffered over the interface.
Handshake lines:
- control byte transfer between devices, using 3-wire handshaking.
- the speed of the data transfer is given by the slowest listener, so every
listener can read bytes transferred over the interface correctly.
- reception of each data byte is acknowledged.
DAV (Data Valid)
- this line is controlled by the Talker
- the talker sets DAV line true (active low) when all devices from bus
release NRFD line (NRFD line high).
- DAV line true means that data byte is stable on the bus (so it can be
read by the listeners).
NRFD (Not Ready For Data)
- this line is controlled by the Listeners to indicate to the Talker if they
are ready to receive new data.
- NRFD line will not go high until all Listeners release the line.
NDAC (Not Data Accepted)
- this line is controlled by the Listeners to indicate to the Talker if data
was read from the bus
- when NDAC line false (high), addressed Listeners indicate that they
read the data from the bus
- NDAC line will not go high until all Listeners release the line.
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