Single wire communications interface and protocol
In a single wire communications interface embodiment, a single wire is coupled between a master device and at least one slave device, the master device configured for transmitting data words as serial data to and for receiving data words as serial data from the at least one slave device, and the at least one slave device configured for transmitting data words as serial data to and receiving data words as serial data from the master device; wherein prior to transmission of any data word on the single wire by one of the master device and the slave device, a sync pulse is first transmitted on the single wire. Integrated circuit embodiments for implementing the single wire communications interface, and method embodiments incorporating the single wire communications interface are disclosed. Additional embodiments are disclosed.
1. A method for communication on a single wire interface, comprising:
receiving, at a receiver coupled to the single wire interface, a sync signal via the single wire interface;
detecting a first signal transition from a first voltage level to a second voltage level of the sync signal, the first signal transition indicating a beginning of a sync pulse of the sync signal;
detecting a second signal transition from the second voltage level to the first voltage level of the sync signal, the second signal transition indicating an end of the sync pulse of the sync signal;
determining whether the sync signal is valid by checking a signal level of the sync signal at a time later than the second signal transition; and
responsive to the determining the sync signal is valid, receiving data via the single wire interface.
2. The method of claim 1 further comprising:
determining a pulse width of the sync pulse of the sync signal by calculating a time period between the first signal transition and the second signal transition; and
receiving bits of data with each data bit being one pulse width wide.
3. The method of claim 2 , in which the calculating a time period between the first signal transition and the second signal transition includes counting a number of cycles of a clock signal internal to the receiver.
4. The method of claim 2 , in which the checking a signal level of the sync signal includes checking at a time that is half that of the pulse width.
5. A method for communication on a single wire interface, comprising:
transmitting, at a transmitter coupled to the single wire interface, a sync signal via the single wire interface with a first signal transition from a first voltage level to a second voltage level, the first signal transition indicating a beginning of a sync pulse of the sync signal,
transmitting a second signal transition from the second voltage level to the first voltage level,
maintaining the second voltage level for a time after the second signal transition to indicate a valid sync pulse; and
transmitting data via the single wire interface after maintaining the second voltage level for the time after the second signal transition.
6. The method of claim 5 further comprising:
determining a pulse width of the sync pulse of the sync signal by calculating a time period between the first signal transition and the second signal transition; and
transmitting data bits after the second transition with each data bit being one pulse width wide.
7. The method of claim 6 , in which calculating a time period between the first signal transition and the second signal transition includes counting a number of cycles of a clock signal internal to the transmitter.
8. The method of claim 6 , in which the maintaining the second voltage level for a time after the second signal transition includes maintaining the second voltage for a time that is half that of the pulse width.
9. The method of claim 5 further comprising:
checking for a conflict for data transmitted via the single wire interface by:
receiving data values for one or more data bits corresponding to a receiver,
comparing the received data values of the receiver with corresponding data values stored in the transmitter, and
determining whether a conflict is detected on the single wire interface based on the comparison results.
10. The method of claim 9 further comprising:
resetting the transmitter and the receiver in response to a determination that a conflict is detected on the single wire interface.
11. The method of claim 5 further comprising:
checking for a stuck state condition of the single wire interface by:
monitoring a voltage level of a wait symbol transmitted via the single wire interface;
counting a number of cycles of a clock signal corresponding to a duration of the wait symbol at the voltage level,
determining the stuck state based on whether the duration of the wait symbol exceeds a threshold duration.
12. The method of claim 11 further comprising:
resetting the transmitter and the receiver in response to the determination of the stuck state of the single wire interface.
13. A device for a two-way one-wire communications system comprising:
the device being configurable as a master or a slave on a two-way communication system, comprising:
a receive buffer configured to receive a sync signal and data via a single wire interface; and
a controller configured to:
detect a first signal transition from a first voltage level to a second voltage level of the sync signal, the first signal transition indicating a beginning of a sync pulse of the sync signal,
detect a second signal transition from the second voltage level to the first voltage level of the sync signal, the second signal transition indicating an end of the sync pulse of the sync signal, and
determine whether the sync signal is valid by checking a signal level of the sync signal at a time later than the second signal transition, wherein the receive buffer is further configured to receive data in response to determining that the sync signal is valid.
14. The device of claim 13 , wherein the controller is further configured to:
determine a pulse width of the sync pulse of the sync signal by calculating a time period between the first signal transition and the second signal transition; and
receive bits of data with each data bit being one pulse width wide.
15. The device of claim 14 further comprising:
a counter configured to calculate the time period by counting a number of cycles of a clock signal internal to the device.
16. The device of claim 14 , including checking a signal level of the sync signal at a time that is half that of the pulse width.
17. The device of claim 13 , wherein the receive buffer receives a sync signal along with each data word received via the single wire interface.
18. The device of claim 13 further comprising:
a transmit buffer configured to transmit data over the single wire interface, the transmit buffer coupled to a transistor, the transistor configured to pull down a voltage level corresponding to the signal wire interface to a reference voltage level.