I had a simple application which POSTs a JSON payload to an API endpoint, running on an STM32 controller with SIM7600EI as the modem.
Shortage of SIM7600EI in the market forced me to switch to 7600CE which is pin by pin compatible with the former. I think the only difference is that the latter lacks some LTE bands. However my POST request fails on the new modem. The modem gets registered on the network and I get the correct responses to the usual status check commands. (CPIN, COPS, CREG, CIPSTAT etc.) Sending SMS also works. Only one relevant LTE band is missing and all network operations here support multiple bands which are available on the modem.
Here's the sequence of commands that I use for an upload: NETCLOSE, CCHMODE=1, CCHSET, =1, CCHSTART, CCHSSLCFG=0,0 CSOCKETPIN=1, CIPMODE=0, NETOPEN, IPADDR, CCHOPEN=0,
All instances of CCHMODE command fails. (Test, read and write). Subsequent commands except CCHSSLCFG work though, but the server doesn't give me an HTTP OK. I have trouble undestanding (what is transparent/data modes?) the purpose of this command, but it seems like it's essential to establish a TLS connection.
SIM7600 series have a common AT command manual which includes this command.
Need this solved on priority. All help is appreciated.
