Echelon Neuron - Manual (Page 124)

SBC (Subtract with Carry)
The SBC instruction subtracts two numbers, and uses the value of the Carry flag
as input to the subtrahend. The SBC instruction uses the direct addressing
mode. The SBC instruction retrieves both TOS and NEXT from the data stack,
adds the value of the Carry flag to TOS, and then subtracts TOS (the
subtrahend) from NEXT (the minuend). TOS and NEXT are consumed, and the
result (the difference) is placed in TOS. The operation modifies the Carry flag as
result of the unsigned subtraction: if the value of TOS plus the value of the
Carry flag exceeds the value of NEXT (indicating that the result would be
negative), the SBC instruction sets the Carry flag; otherwise the instruction
clears the Carry flag.
The SBC instruction applies to Series 3100, 5000, and 6000 devices.
Syntax:
The SBC instruction requires two operands:
SBC NEXT,TOS
Table 48 describes the attributes of the SBC instruction.
Table 48. SBC Instruction
Instruction Hexadecimal
Opcode
Instruction
Size (Bytes)
CPU Cycles
Required
Affect on
Carry Flag
SBC NEXT,TOS 56 1 4 Used, modified
Example:
The following example performs the operation 3-2. The example assumes that
the Carry flag is not set.
pushs #3 ; (3, -, -)
pushs #2 ; (2, 3, -)
sbc next,tos ; (1, -, -)
The value of TOS after this code executes is 1 because (3+Carry)-2 = 1. In this
case, the value of the Carry flag is used for the subtraction, and then modified
(cleared) because the unsigned subtraction did not require an extra carry bit.
114 Neuron Assembly Language Instruction Statements