Upgrading from RN4020 to RN4871

 

 I am in the process of upgrading the wireless interface for those people who want to install it.   I was hoping that moving from the RN4020 to the RN4871 would be simple and painless.  As is always the case now, it was not.

I use the ASCII interface over a standard serial UART.  While most of the commands are the same, there are changes.

1. They have included a delimiter on all GATT messages (%) plus a few others.  While it makes the parsing a little easier, it changed the way the parser worked.  
2. The RN4871 is very sensitive to power and the reset input (see this post).  When I designed Brick Controller 3, I used the PIC nMCLR input to reset the RN4871.  This in turn is driven by TC54 reset controller.  So that part is good, since it appears the RC type resets don't work.  I do have a spare GPIO now, so I could cut/jump that in if it becomes necessary.
3. There is a transparent UART mode, but I am not sure how much Android work that will entail, if it is even possible.
4. The most important change was the elimination of the real time read mode.  The mode would send a message across the UART that the phone was about to read the characteristic.  This would allows the PIC just enough time to update the characteristic value before the phone read it.  That is not implemented in the RN4871.  So I am looking at other ways to do this.

I mostly have the interface working.  It seems to be stable, though the code needs some work.  The 18F26Q71 running at 64MHz, is just too fast for a 115200 baud rate.  During initialization, I have to make sure that the RN4871 response has come in before moving on to another command.  While this implemented in essentially "wait for it to happen" code, this needs to move into the switch function of the BT_TASKS subroutine of the main loop.