I had this problem with a 452 which stumped me for some time. I
still don't know why the PIC should do this. I've checked manuals
and errata but find no mention of a connection between ADCON1
and PortB. Tried this on four 452s and three LCDs, same thing

A 4-bit LCD is on PortB and 1 analogue i/p on PortA. No inputs
are floating, no shorts, no nothing. Once code is running properly
everything works as expected

If ADCON1 is set (to 0x07 digitals) before TRISB, no problem. 
ADC and LCD work fine together. If ADCON1 is set after TRISB,
the code hangs in the Busy routine and flow never returns from LCD
initialisation

Is there some subtlety I've missed in the documentation ? Normally
I have port code in the order as below so never experienced this
before. More of a curiousity than a show-stopper now I realise
what happened. Wish I'd realised at 4am the other morning ;-) !!!

TIA

========================

#define  busy    portb,7
#define  rs      porte,0
#define  rw      porte,1
#define  en      porte,2

;PortB 4-7 - LCD data

         mov     0x07,adcon1

         mov     b'00001001',trisa
;                      1             opto input
;                         1          4-20mA i/p
         movwf   dig_out0a          ;output mask, clear
         xorlw   b'00011111'        ;output mask, set
         movwf   dig_out1a

         mov     b'00000111',trisb
;                  0000              LCD data
;                       1            pushbutton
;                        1           Ring
;                         1          external tick
         movwf   dig_out0b          ;output mask, clear
         xorlw   b'11111111'        ;output mask, set
         movwf   dig_out1b

(further down in code)

         mov     b'11001110',adcon1
;                  1              right-justified
;                   1             Fosc/64 high bit
;                      1110       a.0 as analogue

(further down still)

         mov    b'10000111',trisb   ;b7 as i/p
         bsf    en
rdbusy   btfsc  busy                ;wait for Busy Flag clear
         bra    rdbusy
         bcf    en
         nop
         nop
         bcf    rw
         mov    b'00000111',trisb   ;b7 as o/p
         return

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