DL05 CTRIO2 Binary Math: Configuring 32-Bit Addition

A DL05 can add a 16-bit binary offset to the H0-CTRIO2's unscaled 32-bit binary counter without converting the counter to BCD. Load the double-word count into the 32-bit accumulator, execute ADDB with a binary constant no greater than KFFFF, and store the 32-bit result with OUTD. Do not apply the BCD instruction ADDD directly to a binary counter value.

Why ADDD Fails with an Unscaled CTRIO2 Count

The unscaled H0-CTRIO2 counter value is binary, while ADDD performs BCD arithmetic. Mixing these representations may appear to work at low counts, but it is not valid arithmetic.

The immediate failure point occurs when any four-bit nibble in the binary counter contains a value greater than 9. That bit pattern is invalid BCD, so the BCD instruction refuses the operation. Even binary values whose current bit patterns happen to be valid BCD digits do not make the mixed-format calculation reliable.

Use the DL05 32-Bit Accumulator with ADDB

The DL05 math accumulator is always 32 bits wide. The “double” designation describes the operand added to the accumulator, not the accumulator width. Therefore, ADDB can add a 16-bit binary operand to a 32-bit count already loaded into the accumulator; the result remains available as a 32-bit value.

LDD  V2000
ADDB K1
OUTD V2002

In this sequence, LDD loads the 32-bit counter from V2000, ADDB adds a 16-bit binary constant, and OUTD writes the 32-bit result to V2002. The binary operand must not exceed KFFFF, equivalent to unsigned decimal 65535.

Convert a Decimal Offset to the Binary Constant

Binary addition requires a hexadecimal constant. If the required offset is decimal 360, convert it before entering the operand:

Here, K168 is the hexadecimal representation of decimal 360 for the binary instruction. Using K360 with ADDD instead changes both the instruction's arithmetic format and the operand interpretation; it does not provide valid binary addition to the CTRIO2 count.

When BCD Conversion Is Appropriate

BCD arithmetic is slower than binary arithmetic and reduces the available numeric range. Use BCD only when the surrounding logic or interface requires it. For a binary counter plus an offset within the 16-bit operand limit, retain the binary representation and use ADDB.

Implementation and Verification Procedure

1. Confirm that the H0-CTRIO2 channel is delivering its unscaled binary counter value rather than scaled BCD output.
2. Load the complete double word with LDD; do not load only one word of the counter.
3. Convert the desired positive decimal offset to hexadecimal and confirm that it does not exceed KFFFF.
4. Add the offset with ADDB, then store the accumulator with OUTD.
5. Monitor the source double word and destination double word. Verify that the destination equals the binary source count plus the intended decimal offset across counts whose bit patterns contain hexadecimal digits A through F. This test exposes logic that incorrectly uses BCD arithmetic.

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