Did you ever get this working?? I am trying the same thing on a mangOH red with a WP8548 ( and an HL7748). I can send AT commands all day via tera term, but am wanting to send AT commands via an external MCU via UART1 on the IOT connector. (or any connector where this will work. I have tried the Raspberry Pi connector too). I have not had any success when trying to send “AT” and expecting to get an “OK” back. When I send AT!MAPUART? to the WP8548 via tera term, it returns 1,16, which means AT commands are routed via UART1 and UART2 is going to the Linux console. UART1 is routed to IOT, but I do not get any responses when I use IOT to send AT commands.
I posed this question to our vendor who suggested using Sierra Wireless chips for this project,and he forwarded it on to them and got a response …
“The default method of communication on HL/WP cell modems is a USB connection (UART commands over VCOM port). Unfortunately they need to issues commands via USB to enable AT commands on UART”.
I could understand this on the WP chip, but what is the point of this on the HL when its main communication is via UART? I am about to write back and ask more about how to be able to configure the chips via USB to get the AT commands to work via UART, but it will probably take a week to get a reply. If anyone has any information on this, would be grateful. We might have to switch chips if we cant talk to these via UART from POR.