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Scott McDermott
Scott McDermott

Reputation: 120

Cannot connect UART to RB6 on PIC24FJ128GA204

Using the RPOR registers, I can successfully connect RB3 or RB15 or other pins to a UART (1-4) ... but not RB6. I don't see anything in the documentation or errata that say RB6 (RP6) is uniquely unavailable. Any guesses?

Here are my RPOR registers when I have RB3, RB6, and RC3 all connected to UART0. RB3 and RC3 operate correctly, but RB6 only operates as a digital output.

03D6    RPOR0   0x0000  0       00000000 00000000   '..'
03D8    RPOR1   0x0300  768     00000011 00000000   '..'
03DA    RPOR2   0x0000  0       00000000 00000000   '..'
03DC    RPOR3   0x0003  3       00000000 00000011   '..'
03DE    RPOR4   0x0000  0       00000000 00000000   '..'
03E0    RPOR5   0x0000  0       00000000 00000000   '..'
03E2    RPOR6   0x0000  0       00000000 00000000   '..'
03E4    RPOR7   0x0000  0       00000000 00000000   '..'
03E6    RPOR8   0x0000  0       00000000 00000000   '..'
03E8    RPOR9   0x0300  768     00000011 00000000   '..'
03EA    RPOR10  0x0000  0       00000000 00000000   '..'
03EC    RPOR11  0x0700  1792    00000111 00000000   '..'
03EE    RPOR12  0x0008  8       00000000 00001000   '..'

Here is how PORTB is set up:

018A    TRISB   0x22A2  8866    00100010 10100010   '"¢'
018C    PORTB   0x00C8  200     00000000 11001000   '.È'
018E    LATB    0x0040  64      00000000 01000000   '.@'
0190    ODCB    0x0000  0       00000000 00000000   '..'
0192    ANSB    0x2000  8192    00100000 00000000   '..'

... and here are the CONFIG bits:

_CONFIG1(JTAGEN_OFF & GCP_OFF & GWRP_OFF & ICS_PGx1 & FWDTEN_ON & WINDIS_OFF & FWPSA_PR128 & WDTPS_PS1024);
_CONFIG2(IESO_ON & WDTCMX_LPRC & FNOSC_FRC & FCKSM_CSDCMD & OSCIOFCN_ON & POSCMD_NONE)
_CONFIG3(SOSCSEL_ON)
_CONFIG4(IOL1WAY_OFF & PLLDIV_DISABLED & DSWDTPS_DSWDTPS15)

I am trying to get on the Microchip fora to ask this, but their registration process is apparently down. Hoping the good folks of StackOverflow can help. Thanks!

Upvotes: 2

Views: 281

Answers (2)

Richard Woodham
Richard Woodham

Reputation: 1

I contacted Microchip support and they got back to me in a time considerably shorter than that of proton decay (about a day) with a solution which works.

Bit 11 of FLASH CONFIGURATION WORD 2 (reserved, reset value=1) has to be cleared by appending & 0xF7FF to the config2 setting, like this:

_CONFIG2(POSCMD_NONE & WDTCLK_FRC & OSCIOFCN_OFF & FCKSM_CSDCMD & FNOSC_FRC & ALTCMPI_CxINC_RX & WDTCMX_WDTCLK & IESO_OFF & 0xF7FF)

You will have to live with the compiler warning "consider migrating to #pragma config". The #pragma syntax seems to take text arguments, so really doesn't want you to go flipping undocumented bits.

Quite why peripheral outputs on RB6 are disabled by an undocumented (outside Microchip) bit is beyond me.

Quite why Microchip (or whoever designed the Demo board) chose to use RB6 as TX to the mikroBUS™ Interface is beyond me.

Upvotes: 0

Dan1138
Dan1138

Reputation: 1225

Microchip, with infinite and God like wisdom, decided to have analog input functionality on the RB6 input but suppress almost all documentation of this and remove any mention of this in the PIC24FJ128GA204 errata.

The the data sheet has vague hints about this here:

enter image description here

And here:

enter image description here

To get what you need clear ANSB bit 6 to zero.

Upvotes: 2

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