The HSEROUT command is probably setting the tris register for the operator to make things easy
No it seems not , I have done a bit more experimenting and the chip works as per the data sheet ie
Setting the SPEN bit of the
RCSTA register enables the EUSART and automatically
configures the TX/CK I/O pin as an output.
seting or clearing the tris bit has no effect on the eusart ,

this int driven background printing demo works just fine when trisc.4 is set or not


clearing bits 4:5 of ANSELC does no good as they are not implemented
correct , that saves a couple of words (don't know how I missed that ) and what you say about APFCON makes sense if it can affect the bootloader


Code:
'****************************************************************
'*  Name    : PRINT_16_TX_INT.pbp                                *
'*  Author  : richard                                   *
'*  Notice  :                                *
'*          :                                *
'*  Date    :                                          *
'*  Version :    16f1825                                   *
'*  Notes   :       *
'*          :              *
'*            
'****************************************************************
  
#CONFIG
             __config        _CONFIG1,    _FOSC_INTOSC & _CP_OFF & _WDTE_OFF &  _PWRTE_ON  &  _MCLRE_ON  & _CLKOUTEN_OFF
              __config      _CONFIG2, _PLLEN_OFF & _LVP_OFF
#ENDCONFIG
DEFINE LOADER_USED 1
DEFINE OSC 32
 
include "dt_ints-14.bas"
include "REENTERPBP.bas"
 
asm
INT_LIST macro
       INT_HANDLER TX_INT  , _do_tx, PBP,no
      
      endm
      INT_CREATE
ENDASM

 
RCSTA = $90   ' Enable serial port & continuous receive
TXSTA = $20   ' Enable transmit, BRGH = 0
SPBRG = 51    ' 38400 Baud @ 32MHz, 0.16%
SPBRGH = 0
BAUDCON.3 = 1 ' Enable 16 bit baudrate generator

prnb var byte[32] bank0 
spos var byte bank0
rpos var byte bank0
maxq con 31
HEAD VAR BYTE [70]
I VAR BYTE
J VAR BYTE 
K VAR BYTE
PASS VAR WORD    
led var latc.0
TRISA=%111111
TRISC=%111110
OSCCON=$f0
ANSELA=0
ANSELC=0

CLEAR
while !OSCSTAT.6
wend 
LED=0
INTCON=$C0
   
ARRAYWRITE head, [ "Ready",9,"%",bin6 trisc,13,10,0] 
GOSUB MYPRINT
ARRAYWRITE head,  [ "still",9,"%",bin6 trisc,13,10,0] 
GOSUB MYPRINT  
mainloop:
pause 500 
ARRAYWRITE head,  [ "still Enable 16 bit baudrate generator ",0] 
GOSUB MYPRINT
ARRAYWRITE head,  [ "PASS Enable 16 bit baudrate generator",9,#PASS,13,10,0] 
GOSUB MYPRINT
PASS=PASS+1
goto mainloop 
 
 

MYPRINT:
    J=0
    WHILE HEAD[J]
        INTCON=0
        I=SPOS+1
        K=RPOS
        IF ((I)==K) || ((I== MAXQ )&& !K )  THEN 
            INTCON=$C0
            PAUSE 20
            led=!led
        ELSE
        PRNB[SPOS]= HEAD[J]
        SPOS=SPOS+1
        PIE1.4=1
        IF SPOS=MAXQ THEN SPOS=0
        J=J+1
        ENDIF
        INTCON=$C0
    WEND   
 RETURN
 
 
 
:do_tx 
  IF  RPOS == SPOS THEN
      PIE1.4=0
      ELSE
      IF  PRNB[RPOS] THEN
        TXREG=PRNB[RPOS]
        RPOS=RPOS+1 
        if rpos==maxQ then rpos=0
      ENDIF  
  ENDIF
 @ INT_RETURN