Return to Answer

    mov al,'F'  ; file not found; display blinking 'F'

; 'hide' the next 2-byte instruction by converting it to CMP AX,NNNN
; I learned this trick from Microsoft's Color Computer BASIC :)
    db 3Dh
disk_error:
    mov al,'R'  ; disk read error; display blinking 'R'
error:
```

    mov al,'F'  ; file not found; display blinking 'F'

; 'hide' the next 2-byte instruction by converting it to CMP AX,NNNN
; I learned this trick from Microsoft's Color Computer BASIC :)
    db 3Dh
disk_error:
    mov al,'R'  ; disk read error; display blinking 'R'
error:

Finally, here's a very similar use of a skipping instruction in DOSLFN Version 0.41c (11/2012). Instead of test ax, imm16 they're using mov cx, imm16 which has no effect on the status flags but clobbers the cx register instead. (Opcode 0B9h is mov ecx, imm32 in non-16-bit modes, and writes to the full ecx or rcx register.)

;THROW-Geschichten... [english: THROW stories...]
SetErr18:
        mov     al,18
        db      0B9h            ;mov cx,nnnn
SetErr5:
        mov     al,5
        db      0B9h            ;mov cx,nnnn
SetErr3:
        mov     al,3
        db      0B9h            ;mov cx,nnnn
SetErr2:
        mov     al,2
SetError:

Further, here's a very similar use of a skipping instruction in DOSLFN Version 0.41c (11/2012). Instead of test ax, imm16 they're using mov cx, imm16 which has no effect on the status flags but clobbers the cx register instead. (Opcode 0B9h is mov ecx, imm32 in non-16-bit modes, and writes to the full ecx or rcx register.)

;THROW-Geschichten... [english: THROW stories...]
SetErr18:
        mov     al,18
        db      0B9h            ;mov cx,nnnn
SetErr5:
        mov     al,5
        db      0B9h            ;mov cx,nnnn
SetErr3:
        mov     al,3
        db      0B9h            ;mov cx,nnnn
SetErr2:
        mov     al,2
SetError:

Finally, the FAT12 boot loader released on 2002-11-26 as fatboot.zip/fat12.asm by Chris Giese (which I based my FAT12, FAT16, and FAT32 loaders on) uses cmp ax, imm16 as a skipping instruction in its error handler. This is similar to my lDOS boot error handlers but cmp leaves an indeterminate Carry Flag state rather than always setting up No Carry. Also note the comment referring to "Microsoft's Color Computer BASIC":

    mov al,'F'  ; file not found; display blinking 'F'

; 'hide' the next 2-byte instruction by converting it to CMP AX,NNNN
; I learned this trick from Microsoft's Color Computer BASIC :)
    db 3Dh
disk_error:
    mov al,'R'  ; disk read error; display blinking 'R'
error:
```

11: Skipping instructions

The constants __TEST_IMM8, __TEST_IMM16, and __TEST_OFS16_IMM8 are defined to the respective byte strings for these instructions. They can be used to skip subsequent instructions that fit into the following 1, 2, or 3 bytes. However, note that they modify the flags register, including always setting NC. The 16-bit offset plus 16-bit immediate test instruction is not included for these purposes because it might access a word at offset 0FFFFh in a segment. Also, the __TEST_OFS16_IMM8 as provided should only be used in 86M, to avoid accessing data beyond a segment limit. After the db instruction using one of these constants, a parenthetical remark should list which instructions are skipped.

=== snip .success: db __TEST_IMM8 ; (NC) .error: stc retn === snip

11: Skipping instructions

The constants __TEST_IMM8, __TEST_IMM16, and __TEST_OFS16_IMM8 are defined to the respective byte strings for these instructions. They can be used to skip subsequent instructions that fit into the following 1, 2, or 3 bytes. However, note that they modify the flags register, including always setting NC. The 16-bit offset plus 16-bit immediate test instruction is not included for these purposes because it might access a word at offset 0FFFFh in a segment. Also, the __TEST_OFS16_IMM8 as provided should only be used in 86M, to avoid accessing data beyond a segment limit. After the db instruction using one of these constants, a parenthetical remark should list which instructions are skipped.

.success:
        db __TEST_IMM8                  ; (NC)
.error:
        stc
        retn