AC4490 Hardware Integration Guide
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Pin Descriptions
Generic I/O
Both GI0/1 pins serve as generic input pins and both GO0/1 pins server as generic output pins. Reading and
writing of these pins can be performed using CC Commands. These pins alternatively serve as control pins
when modem mode is enabled.
TXD & RXD
Serial TTL
The AC4490-200 accepts 3.3 or 5 V DC TTL level asynchronous serial data on the RXD pin and
interprets that data as either command data or transmit data. Data is sent from the transceiver,
at 3.3V levels, to the OEM host via the TXD pin.
Note: The AC4490-1000 and AC4490-1x1 transceivers only accept 3.3 V level signals.
CTS
The AC4490 has an interface buffer size of 256 bytes. If the buffer fills up and more bytes are sent to the
transceiver before the buffer can be emptied, data loss occurs. The transceiver prevents this loss by asserting
CTS High as the buffer fills up and asserting CTS Low as the buffer is emptied. CTS On and CTS On Hysteresis
control the operation of CTS. CTS On specifies the amount of bytes that must be in the buffer for CTS to be
disabled (logic High). Even while CTS is disabled, the OEM host can send data to the transceiver, but it should
do so carefully.
Note: The CTS On and CTS On Hysteresis bytes of the EEPROM can be set to 1, in which case CTS goes
high as data is sent in and low when the buffer is empty.
GND
Signal Ground. Pins are internally connected.
RTS
With RTS disabled, the transceiver sends any received data to the OEM host when it is received. However,
some OEM hosts are not able to accept data from the transceiver all of the time. With RTS enabled, the OEM
host can prevent the transceiver from sending data by setting RTS logic High. Once RTS is set logic Low, the
transceiver can send packets to the OEM host as they are received.
Note: Leaving RTS logic high for too long can cause data loss once the 256 byte receive buffer fills up.
Test
When pulled logic Low before applying power or resetting, the transceiver’s serial interface is forced to 9600
baud, 8-N-1 (8 data bits, No parity, 1 stop bit). To exit, the transceiver must be reset or power-cycled with
Test pin logic High. This pin is used to recover transceivers from unknown baud rates only. It should not be
used in normal operation. Instead, the transceiver Interface Baud Rate should be programmed to 9600 baud
if that rate is desired for normal operation.
