Specifications

Processor Description (V40)
General Purpose Registers
AW [AX], BW [BX], CW [CX], and DW [DX]
The CPU has four 16-bit general purpose registers. Each of these
registers can be addressed as one 16-bit register or two 8-bit
registers. The 16-bit registers are referred to as AW [AX], BW
[BX], CW [CX], and DW [DX]. The high order bytes of the 16-
bit registers are AH, BH, CH, and DH, while the low order bytes
are AL, BL, CL, and DL. The most common use of these
registers is to provide a temporary storage location for data. Some
instructions do assign specific meanings to the general purpose
registers, as shown in Table 5-2.
Table 5-2
Implied Use of General Registers.
Register Implied Use Register Implied Use
AW [AX]: Word Multiplication/ BW [BX]: Translation
Division
Word Input/Output CW [CX]: String Operations
AL: Byte Multiplication/ CL: Variable Shift
Division and Rotate
Byte Input/Output
Translation DW [DX]: Word Multiplication/
BCD and Decimal Division
Arithmetic Indirect Input/Output
AH: Byte Multiplication/
Division
5-11