Hello,

I am new to PICs and am having trouble initialising the USART on a
16c73a. I only need the use of the transmitter, but am trying to
initialise both TX and RX since I don't know if only one can be used.
Can anyone help? If it matters, I am simulating with MPLAB 4.12. As per
Mark's indications, I am including the following code:

; Intializing PORTC
   BCF      STATUS, RP0    ; Select Bank 0 (for PORTC)
   CLRF     PORTC          ; Clear output data latches
   MOVLW    b'11000000'    ; Initialize data direction
   BSF      STATUS, RP0    ; Select Bank 1 (for TRISC)
   MOVWF    TRISC          ; Set RC<5:0> as outputs, RC<7:6> as inputs
                           ;  RC<7:6> really USART TX and RX

; Initialize the USART
   BSF      STATUS, RP0    ; Bank 1 (SPBRG)
   MOVLW    0x09           ; BRG Control Value
   MOVWF    SPBRG          ;
   BCF      STATUS, RP0    ; Bank 0 (RCSTA)
   MOVLW    b'10010000'    ; SPEN=1, CREN=1
   MOVWF    RCSTA          ;
   BSF      STATUS, RP0    ; Bank 1 (TXSTA)
   BSF      TXSTA, TXEN    ; Enable transmission

The problem is that after I set TXEN, the TXIF bit is not set (it should
be set since the TXREG is empty, shouldn't it?). Later on in my code, I
loop on TXIF, to see if TXREG is empty, but the program gets stuck
there. I tried adding the following code to transmit something first and
then loop on TXIF (maybe TXIF isn't set after TXEN is set (after a reset
that is)):

; Transmit something
   BCF      STATUS, RP0    ; Bank 0 (TXREG)
   MOVLW    0xFF           ;
   MOVWF    TXREG          ;

; Transmit again
   BCF      STATUS, RP0    ; Bank 0 (PIR1 & TXREG)
LOOP
   BTFSS    PIR1, TXIF     ;
   GOTO     LOOP           ;
   MOVLW    0xAA           ;
   MOVWF    TXREG          ;

Once again, the program gets caught in the loop. What am I doing wrong?
I've also tried looping on TRMT (TXSTA<1>), but to avail; actually the
opposite happens - I can always write to TXREG because TRMT is always
set.

Some other oddities I've notice:

1) Although TRMT (TXSTA<1>) is read-only, I can write to it. At least
that's what the simulator indicates - does this have to do with the data
latches (I would hope the simulator would be absolute)?

2) On the general mid-range PIC data sheet (DS31018A), Section 18
(USART), Example 18-2: Asynchronous Transmitter/Receiver, TXSTA is
initiated with 0x40. The comments beside this initialisation is: "8-bit
transmit,  transmitter enabled, asynchronous mode, low speed mode", but
0x40 is: 9-bit transmit, transmitter DISabled, asynchronous mode, low
speed mode. I imagine this example is in error looking at the 16c7x data
sheets (and the page before the code on DS31018A).

Oddity 2) above is especially perplexing since writing 0x40 to TXSTA
would clear TRMT for me (as per oddity number 1) above).

Can anyone help?

Mario