AC4490 Hardware Integration Guide
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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).
You can perform a successful design without monitoring CTS. However, you need to take into
account the amount of latency the radio adds to the system, any additional latency caused by
Transmit Retries or Broadcast Attempts, how often you send data, non-delivery network
timeouts and interface data rate. Polled type networks, where the server host requests data
from the client host and the client host responds, are good candidates for avoiding the use of
CTS. This is because no single transceiver can monopolize the RF link. Asynchronous type
networks, where any radio can send to another radio at any point in time, are much more
difficult to implement without the use of CTS.
