Serial communication protocol
A serial communication protocol for daisy-chained slave devices does away with the requirement for an entire byte of dummy clocks to be cycled between a slave's input and output, instead requiring a shorter set of dummy clock cycles which improves efficiency of a serial communication system. According to a specification of a serial communications protocol, data is exchanged between master and slave devices in communication frames. Each communication frame has a command portion and a data portion, and each respective portion may comprise packages of one or more bytes.
1. A serial communication apparatus, comprising:
a master device having a master input and a master output; and
a plurality of slave devices, each comprising a slave input and a slave output, said plurality being arranged in a daisy chain configuration, wherein a first slave device is arranged to receive data from the master output at its slave input, and one or more successive slave devices are arranged to receive data from a slave output of a preceding slave device, wherein
the master device is arranged to send a communication frame that comprises a sub-byte syllable which selectively triggers transmission of data from a slave input to a slave output, the communication frame including a device address byte defining a slave device address, and said sub-byte syllable being provided as an initial portion of said address byte; and
the triggered transmission of data from slave input to slave output commences before the remainder of the device address byte is received by the slave input.
2. The serial communication apparatus of claim 1 , wherein said sub-byte syllable comprises one bit.
3. The serial communication apparatus of claim 2 , wherein the one bit is held at a first logic value to indicate the beginning of a communication frame.
4. The serial communication apparatus of claim 1 , wherein a final slave device adjusts a delay to ensure that the input to the master device is byte-aligned.
5. The serial communication apparatus of claim 4 , wherein the adjustment of the delay is set by a special command embedded in the communication frame, preferably in the address byte.
6. The serial communication apparatus of claim 4 , wherein the adjustment of the delay is set by a register in the slave device, which has a value that can be set to inform one slave to be byte-aligned.
7. The serial communication apparatus of claim 1 , configured such that each slave device stores its identity to determine its position in the daisy chain of slave devices, and during transmission of a communication frame data, is passed from a slave input to a slave output in the same clock cycle.
8. The serial communication apparatus of claim 7 , configured such that:
during the transmission of an initial communication frame, each slave device is configured to determine its position in the daisy chain based on a delay between the slave input and slave output for that slave;
and thereafter during transmission of subsequent communication frames, data is passed by the slaves from their slave inputs to their slave outputs in the same clock cycle.
9. The serial communication apparatus of claim 1 , comprising a serial peripheral interface.
10. A serial communication apparatus, comprising:
a master device having a master input and a master output; and
a plurality of slave devices, each comprising a slave input and a slave output, said plurality being arranged in a daisy chain configuration wherein a first slave device is arranged to receive data from the master output at its slave input and one or more successive slave devices are arranged to receive data from a slave output of a preceding slave device, wherein
the serial communication apparatus is configured such that:
during the transmission of an initial communication frame each slave device is configured to determine its position in the daisy chain based on a delay between the slave input and slave output for that slave; and
thereafter during transmission of subsequent communication frames, data is passed by the slaves from their slave inputs to their slave outputs in the same clock cycle.
11. The serial communication apparatus of claim 10 wherein the delay between the slave input and slave output is k bytes, where k is the position of the slave in the daisy chain.
12. The serial communication apparatus of claim 10 , wherein the delay between the slave input and slave output is k sub-byte syllables, where k is the position of the slave device in the daisy chain.
13. A method of communicating data between devices in a serial communication apparatus, said serial communication apparatus comprising a master device having a master input and a master output, a plurality of slave devices, each comprising a slave input and a slave output, said plurality being arranged in a daisy chain configuration wherein a first slave device is arranged to receive data from the master output at its slave input and one or more successive slave devices are arranged to receive data from a slave output of a preceding slave device, wherein, according to the method,
the master device sends a communication frame that comprises a sub-byte syllable the communication frame including a device address byte defining a slave device address, and said sub-byte syllable being provided as an initial portion of said address byte; a slave device receives the communication frame at its slave input; and the sub-byte syllable selectively triggers transmission of data from a slave input to a slave output, wherein the triggered transmission of data from slave input to slave output commences before the remainder of the device address byte is received by the slave input.
14. The method of claim 13 , wherein said sub-byte syllable comprises one bit.
15. The method of claim 14 , wherein the one bit is held at a first logic value to indicate the beginning of a communication frame.
16. The method of claim 13 , wherein a final slave device adjusts a delay to ensure that the input to the master device is byte-aligned.
17. The method of claim 16 , wherein the adjustment of the delay is set by a special command embedded in the communication frame, preferably in the address byte.
18. The method of claim 16 , wherein the adjustment of the delay is set by a register in the slave device, which has a value that can be set to inform one slave to be byte-aligned.
19. The method of claim 13 , wherein each slave device stores its identity to determine its position in the daisy chain of slave devices, and during transmission of a communication frame, data is passed from a slave input to a slave output in the same clock cycle.
20. The method of claim 19 , wherein:
during the transmission of an initial communication frame each slave device determines its position in the daisy chain based on a delay between the slave input and slave output for that slave;
and thereafter during transmission of subsequent communication frames, data is passed by the slaves from their slave inputs to their slave outputs in the same clock cycle.
21. The method of claim 13 , being part of a serial peripheral interface protocol.
22. A method of communicating data between devices in a serial communication apparatus, said serial communication apparatus comprising a master device having a master input and a master output, a plurality of slave devices, each comprising a slave input and a slave output, said plurality being arranged in a daisy chain configuration wherein a first slave device is arranged to receive data from the master output at its slave input, and one or more successive slave devices are arranged to receive data from a slave output of a preceding slave device, wherein, according to the method,
during the transmission of an initial communication frame each slave device determines its position in the chain based on a delay between the slave input and slave output for that slave;
and thereafter during transmission of subsequent communication frames, data is passed by the slaves from their slave inputs to their slave outputs in the same clock cycle.
23. The method of claim 22 , wherein the delay between the slave input and slave output is k bytes, where k is the position of the slave in the daisy chain.
24. The method of claim 22 , wherein the delay between the slave input and slave output is k sub-byte syllables, where k is the position of the slave device in the daisy chain.