12f1822, serial RX under interrupt, echo program doesn't want to play

[Mike, K8LH]

Are you missing a bank select in that code snippet?

asm
myint:
    banksel PIR1            '                    |B0
    btfss   PIR1,RCIF       '                    |B0
    goto    int_out         '                    |B0
    bcf     PIR1,RCIF       '                    |B0
    banksel RCREG           '                    |B3
    movfw   RCREG           '                    |B3
    banksel _RX_BYTE        '                    |B?
    movwf   _RX_Byte        '                    |B?
    banksel TXREG           '                    |B3
    movwf   TXREG           '                    |B3
    nop                     '                    |B3
    btfss   PIR1,TXIF       '                    |B0 <-- *****
    goto    $-1             '                    |B0
       
int_out:    
    retfie
endasm

If _RX_Byte is in bank 0, then maybe this would work?

asm
myint:
    banksel PIR1            '                    |B0
    btfss   PIR1,RCIF       '                    |B0
    retfie                  '                    |B0
    bcf     PIR1,RCIF       '                    |B0
    banksel RCREG           '                    |B3
    movfw   RCREG           '                    |B3
    movwf   TXREG           '                    |B3
    banksel _RX_BYTE        '                    |B0
    movwf   _RX_Byte        '                    |B0
    btfss   PIR1,TXIF       '                    |B0
    goto    $-1             '                    |B0
    retfie                  '                    |B0
endasm