Data Sheet

AC4490
Datasheet
https://www.lairdconnect.com/
16
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7 RADIO INTERFACE
7.1 Protocol Status / Receive Acknowledgement
Note: Implemented in firmware v6.3 and later.
When enabled in EEPROM, GO0 and GO1 perform the functions of Protocol Status and Receive Acknowledgement.
7.1.1 Protocol Status
Every time the radio hops to hop bin 0, the radio asserts GO0 Low for the entire hop bin. GO0 goes low at the falling edge of
the hop frame at the start of bin 0 and goes high with the rising edge of hop frame at the end of bin 0. During all other hops,
GO0 is high.
Note: This mode is incompatible with Modem mode.
7.1.2 Receive Acknowledgement
The radio uses GO1 to signal that a valid RF acknowledgement has been received from the remote radio. GO1 is normally low
and goes high within approximately 75 µSec of receiving a valid RF acknowledgement. It remains high until the end (rising
edge) of the next hop.
Note: This mode is incompatible with Modem mode.
7.2 Flow Control
7.2.1 CTS On/CTS On Hysteresis (Flow Control)
Flow control refers to the control of data flow between transceivers. It is the method used to handle data in the transmit/receive
buffer and determines how data flow between the transceivers is started and stopped. Often, one transceiver is capable of
sending data at a higher rate than the other can receive it. Flow control allows the slower device to tell the faster device when
to pause and resume data transmission.
When a transceiver has data to send, it sends a Ready To Send signal and waits for a Clear To Send response from the
receiving unit. If the receiving radio is ready to accept data it will assert its CTS low. CTS will be reasserted when the buffer
contains the number of bytes specified by CTS_OFF (EEPROM address 0x5D). These signals are sent apart from the data
itself on separate wires.
Flow control refers to the control of data flow between transceivers. It is the method used to handle data in the transmit/receive
buffer and determines how data flow between the transceivers is started and stopped. Often, one transceiver is capable of
sending data faster than the other can receive it. Flow control allows the slower device to tell the faster device when to pause
and resume data transmission.
If RTS Enable is enabled, the receiver will monitor RTS. If the OEM asserts its CTS (transceivers RTS) high, the transceiver
will wait to send data over the serial bus to the OEM host until the RTS is asserted low. CTS should be monitored by the OEM
host since this is the manner the transceiver signals the OEM Host that it’s transmit buffer may be full. If it asserts CTS high,
the OEM host should stop sending data over the serial bus. If CTS is asserted low, the OEM host can send data over the
serial bus because the transmit buffer is not at its limit.
Tip: Can I implement a design using just TXD, RXD, and GND (three-wire Interface)?
Yes. However, it is strongly recommended that your hardware monitor the CTS pin of the radio. CTS is taken High
by the radio when its interface buffer is getting full. Your hardware should stop sending at this point to avoid a
buffer overrun (and subsequent loss of data).