Trying to understand Microchip PIC16LF15344 peripheral pin selection for I2C - c

Question

I have been reviewing the Microchip PIC16LF15344 datasheet for peripheral pin selection, and either I am reading it incorrectly or it appears to have errors and inconsistencies in the document. I would like to know if anyone else has used this device and can confirm my interpretation.
I'm trying to write code for a PIC16LF15344 to make use of the I2C interface. I have managed to write I2C code for a PIC16LF1822 that works fine, but I have so far been unable to get this to work on the PIC16LF15344, and there is some confusing documentation in the data sheet that I would like to get cleared up.
Here is a reference to the datasheet.
The pinout descriptions for the PIC16LF15344 shows that the I2C SDA function can be allocated to RC1 or RB6. Likewise, I2C SCL may be allocated to RC0 or RB4. But there is a note in Section 15.3 Bidirectional Pins as follows.
The I2C SCLx and SDAx functions can be remapped through PPS. However, only the RB1, RB2, RC3, and RC4 pints have the I2C and SMBus specific input buffers implemented (I2C mode disables INLVL and sets thresholds that are specific for I2C). If the SCLx or SDAx functions are mapped to some other pin (other than RB1, RB2, RC3, or RC4), the general purpose TTL or ST input buffers (as configured based on INLVL register setting) will be used instead. In most applications, it is therefore recommended only to map the SCLx and SDAx pin functions to the RB1, RB2, RC3 or RC4 pins.
The problem is not only does the note appear to conflict with the descriptions in the pin allocation tables, it also references pins RB1 and RB2, which don't appear anywhere in the pin allocation tables, i.e., they don't appear to exist for this PIC. I see similar footnote references to RB1 and RB2, but they are not documented anywhere in the body of the document or the tables.
Certainly this must be a documentation error, but I can find no current errata on the PIC16LF15324/44 datasheet to correct this. Am I reading this right?
I have tried configuring SCL and SDA with PPS to pins RC0 and RC1, since that is how they are wired on my PCB, but I can't get the I2C working yet using essentially the same software that I was using for the PIC16LF1822. The PPS default for EUSART TX2 and RX2 are RC0 and RC1. Does that mean I need to use TX2CKPPS and RX2DTPPS to move the EUSART assignments elsewhere before using SSP1CLKPPS and SSP1DATPPS to assign SCL and SDA to RC0 and RC1?
I will be investigating other potential problems with my PCB, but I want to get this straightened out before I submit another PCB for fab. I need to make some changes anyway, so I might just connect SCL and SDA to their PPS defaults in the next version and try again.
Here is the initialization code:
OSCFRQbits.HFFRQ = 0b011; // Set internal HF oscillator frequency to 8 MHz
WPUA = 0b00111111; // Enable all weak pull-up resistors on port A
WPUB = 0b11110000; // Enable all weak pull-up resistors on port B
WPUC = 0b11111100; // Enable all weak pull-up resistors on port C except
// RC0 and RC1 to be used as I2C SCL and SDA
TRISA = 0b00110000; // Set RA4 and RA5 as inputs
ANSELA = 0b00110000; // Set RA4 and RA5 to analog
TRISB = 0b00110000; // Set RB6 and RB7 as inputs
ANSELB = 0b11000000; // Set RB6 and RB7 as analog
TRISC = 0b11111011; // Set RC0, RC1, RC3, RC4, RC5, RC6, and RC7 as inputs
ANSELC = 0b11111000; // Set RC3, RC4, RC5, RC6, and RC7 as analog
TX2CKPPS = 0b01100; // Use RB4 for TX2
RX2DTPPS = 0b01110; // Use RB6 for RX2
SSP1CLKPPS = 0b10000; // Use RC0 as SCL
SSP1DATPPS = 0b10001; // Use RC1 as SDA
SSP1CON1 = 0b00100110; // SSPEN enabled, WCOL no collision, SSPOV no overflow,
// CKP low hold, SSPM I2C slave 7-bit
SSP1CON2 = 0b00000000; // ACKSTAT received, RCEN disabled, RSEN disabled,
// ACKEN disabled, ACKDT acknowledge, SEN disabled,
// GCEN disabled, PEN disabled
SSP1CON3 = 0b00000000; // BOEN disabled, AHEN disabled, SBCDE disabled,
// SDAHT 100 ns hold, ACKTIM ackseq, DHEN disabled,
// PCIE disabled, SCIE disabled
SSP1STAT = 0x00;
SSP1BUF = 0x00;
SSP1MSK = 0xff;
SSP1ADD = I2C_SLAVE_ADDR << 1;
PIR3bits.SSP1IF = 0; // Clear the SSP Interrupt flag
PIE3bits.SSP1IE = 1; // Enable SSP Interrupts
INTCONbits.GIE = 1; // Enable global interrupts
INTCONbits.PEIE = 1; // Enable peripheral interrupts

Answer 1

You likely have several issues to deal with.
All of the default I2C pins also have analog functionality too. Be sure that the ANSB or ANSC bits that are associated with the I2C pins are setup for digital operation.
While the power on reset selects the data sheet defaults for the I2C input pin assignments the I2C outputs by default are not assigned to any GPIO pin. You will need to place the I2C outputs for SCL and SDA in the correct PPS mapping registers.
Note that regardless of the I2C master or slave implementation both the input and output functions should be mapped to the same pin.
It would help to edit your question and post the code that you use to initialize the I2C pins and PPS mapping registers.
/*
* File: main.c
* PIC16LF15354
* +-------------:_:-------------+
* 10K Pull-Up -> 1 : RE3/MCLR ANB7/RX2/PGD/RB7 : 28 <>
* <> 2 : RA0/ANA0 ANB6/TX2/PGC/RB6 : 27 <> RX2
* <> 3 : RA1/ANA1 ANB5/RB5 : 26 <>
* <> 4 : RA2/ANA2 ANB4/RB4 : 25 <> TX2
* <> 5 : RA3/ANA3 ANB3/RB3 : 24 <>
* <> 6 : RA4/ANA4 ANB2/SDA2/RB2 : 23 <>
* <> 7 : RA5/ANA5 ANB1/SCL2/RB1 : 22 <>
* GND -> 8 : VSS ANB0/RB0 : 21 <>
* <> 9 : RA7/OSC1/ANA7 VDD : 20 <- 3v3
* <> 10 : RA6/OSC2/ANA6 VSS : 19 <- GND
* SCL1 <> 11 : RC0/ANC0 ANC7/RX1/RC7 : 18 <>
* SDA1 <> 12 : RC1/ANC1 ANC6/TX1/RC6 : 17 <>
* <> 13 : RC2/ANC2 ANC5/RC5 : 16 <>
* <> 14 : RC3/SCL1/ANC3 ANC4/SDA1/RC4 : 15 <>
* +-----------------------------:
* DIP-28
*
* Created on January 4, 2019, 6:20 PM
*/
// PIC16LF15354 Configuration Bit Settings
#pragma config FEXTOSC = OFF // External Oscillator mode selection bits (Oscillator not enabled)
#pragma config RSTOSC = HFINT32 // Power-up default value for COSC bits (HFINTOSC with OSCFRQ= 32 MHz and CDIV = 1:1)
#pragma config CLKOUTEN = OFF // Clock Out Enable bit (CLKOUT function is disabled; i/o or oscillator function on OSC2)
#pragma config CSWEN = ON // Clock Switch Enable bit (Writing to NOSC and NDIV is allowed)
#pragma config FCMEN = OFF // Fail-Safe Clock Monitor Enable bit (FSCM timer disabled)
#pragma config MCLRE = ON // Master Clear Enable bit (MCLR pin is Master Clear function)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config LPBOREN = OFF // Low-Power BOR enable bit (ULPBOR disabled)
#pragma config BOREN = OFF // Brown-out reset enable bits (Brown-out reset disabled)
#pragma config BORV = LO // Brown-out Reset Voltage Selection (Brown-out Reset Voltage (VBOR) set to 1.9V on LF, and 2.45V on F Devices)
#pragma config ZCD = OFF // Zero-cross detect disable (Zero-cross detect circuit is disabled at POR.)
#pragma config PPS1WAY = OFF // Peripheral Pin Select one-way control (The PPSLOCK bit can be set and cleared repeatedly by software)
#pragma config STVREN = ON // Stack Overflow/Underflow Reset Enable bit (Stack Overflow or Underflow will cause a reset)
#pragma config WDTCPS = WDTCPS_31// WDT Period Select bits (Divider ratio 1:65536; software control of WDTPS)
#pragma config WDTE = SWDTEN // WDT operating mode (WDT enabled/disabled by SWDTEN bit in WDTCON0)
#pragma config WDTCWS = WDTCWS_7// WDT Window Select bits (window always open (100%); software control; keyed access not required)
#pragma config WDTCCS = SC // WDT input clock selector (Software Control)
#pragma config BBSIZE = BB512 // Boot Block Size Selection bits (512 words boot block size)
#pragma config BBEN = OFF // Boot Block Enable bit (Boot Block disabled)
#pragma config SAFEN = OFF // SAF Enable bit (SAF disabled)
#pragma config WRTAPP = OFF // Application Block Write Protection bit (Application Block not write protected)
#pragma config WRTB = OFF // Boot Block Write Protection bit (Boot Block not write protected)
#pragma config WRTC = OFF // Configuration Register Write Protection bit (Configuration Register not write protected)
#pragma config WRTSAF = OFF // Storage Area Flash Write Protection bit (SAF not write protected)
#pragma config LVP = OFF // Low Voltage Programming Enable bit (High Voltage on MCLR/Vpp must be used for programming)
#pragma config CP = OFF // UserNVM Program memory code protection bit (UserNVM code protection disabled)
#include <xc.h>
#define I2C_SLAVE_ADDR 0x00
void main(void)
{
WPUA = 0b00111111; // Enable all weak pull-up resistors on port A
WPUB = 0b11110000; // Enable all weak pull-up resistors on port B
WPUC = 0b11111100; // Enable all weak pull-up resistors on port C except
// RC0 and RC1 to be used as I2C SCL and SDA
TRISA = 0b00110000; // Set RA4 and RA5 as inputs
ANSELA = 0b00110000; // Set RA4 and RA5 to analog
TRISB = 0b00110000; // Set RB6 and RB7 as inputs
ANSELB = 0b11000000; // Set RB6 and RB7 as analog
TRISC = 0b11111011; // Set RC0, RC1, RC3, RC4, RC5, RC6, and RC7 as inputs
ANSELC = 0b11111000; // Set RC3, RC4, RC5, RC6, and RC7 as analog
#ifdef WRONG_WAY_TO_DO_PPS
TX2CKPPS = 0b01100; // Use RB4 for TX2
RX2DTPPS = 0b01110; // Use RB6 for RX2
SSP1CLKPPS = 0b10000; // Use RC0 as SCL
SSP1DATPPS = 0b10001; // Use RC1 as SDA
#else
RB4PPS = 0x11; // Assign TX2 output to RB4
RX2DTPPS = 0x0E; // Assign RB6 to RX2 input
RC0PPS = 0x15; // Assign SCL1 output to RC0
SSP1CLKPPS = 0x10; // Assign RC0 to SCL1 input
RC1PPS = 0x16; // Assign SDA1 output to RC1
SSP1DATPPS = 0x11; // Assign RC1 to SDA1 input
#endif
SSP1CON1 = 0b00100110; // SSPEN enabled, WCOL no collision, SSPOV no overflow,
// CKP low hold, SSPM I2C slave 7-bit
SSP1CON2 = 0b00000000; // ACKSTAT received, RCEN disabled, RSEN disabled,
// ACKEN disabled, ACKDT acknowledge, SEN disabled,
// GCEN disabled, PEN disabled
SSP1CON3 = 0b00000000; // BOEN disabled, AHEN disabled, SBCDE disabled,
// SDAHT 100 ns hold, ACKTIM ackseq, DHEN disabled,
// PCIE disabled, SCIE disabled
SSP1STAT = 0x00;
SSP1BUF = 0x00;
SSP1MSK = 0xff;
SSP1ADD = I2C_SLAVE_ADDR << 1;
PIR3bits.SSP1IF = 0; // Clear the SSP Interrupt flag
PIE3bits.SSP1IE = 1; // Enable SSP Interrupts
INTCONbits.GIE = 1; // Enable global interrupts
INTCONbits.PEIE = 1; // Enable peripheral interrupts
/*
* Embedded code never returns from main
*/
for(;;)
{
}
}
The PPS is setup correctly but I do not know if the I2C initialization code is right.