AMD Am188TMER, Am186TMER user manual Programming, Register SET

CHAPTER

2 PROGRAMMING

All members of the Am186 and Am188 family of microcontrollers, including the Am186ER and Am188ER, contain the same basic set of registers, instructions, and addressing modes, and are compatible with the original industry-standard 186/188 parts.

2.1REGISTER SET

The base architecture of the Am186ER and Am188ER microcontrollers has 14 registers, as shown in Figure 2-1.These registers are grouped into the following categories:

νGeneral Registers—Eight 16-bit general purpose registers can be used for arithmetic and logical operands. Four of these (AX, BX, CX, and DX) can be used as 16-bit registers or split into pairs of separate 8-bit registers (AH, AL, BH, BL, CH, CL, DH, and DL). The Destination Index (DI) and Source Index (SI) general-purpose registers are used for data movement and string instructions. The Base Pointer (BP) and Stack Pointer (SP) general-purpose registers are used for the stack segment and point to the bottom and top of the stack, respectively.

–Base and Index Registers—Four of the general-purpose registers (BP, BX, DI, and SI) can also be used to determine offset addresses of operands in memory. These registers can contain base addresses or indexes to particular locations within a segment. The addressing mode selects the specific registers for operand and address calculations.

–Stack Pointer Register—All stack operations (POP, POPA, POPF, PUSH, PUSHA, PUSHF) utilize the stack pointer. The Stack Pointer Register is always offset from the Stack Segment (SS) Register, and no segment override is allowed.

νSegment Registers—Four 16-bit special-purpose registers (CS, DS, ES, and SS) select, at any given time, the segments of memory that are immediately addressable for code (CS), data (DS and ES), and stack (SS) memory. (For usage, refer to section 2.2.)

νStatus and Control Registers—Two 16-bit special-purpose registers record or alter certain aspects of the processor state—the Instruction Pointer (IP) Register contains the offset address of the next sequential instruction to be executed and the Processor Status Flags (FLAGS) Register contains status and control flag bits (see Figure 2-1and Figure 2-2).

Note that the Am186ER and Am188ER microcontrollers have additional on-chip peripheral registers, which are external to the processor. These external registers are not accessible by the instruction set. However, because the processor treats these peripheral registers like memory, instructions that have operands that access memory can also access peripheral registers. The above processor registers, as well as the additional on-chip peripheral registers, are described in the chapters that follow.

Programming 2-1