SEL-2890 Instruction Manual Date Code 20210715
Firmware Upgrade Instructions
Upgrade Procedure
B.4
b. Restart the SEL-2890. Repeat the AT+++ sequence three or
more times. If the SEL-2890 is still unresponsive and you
have tried the original and default data rate of 19200, then go
to Step c.
c. The transceiver firmware upgrade was unsuccessful and the
transceiver will require factory servicing before it can be
returned to service.