OVERVIEW OF THE 80C186 FAMILY ARCHITECTURE
2-36
Figure 2-21. String Operand
2.2.2.3
I/O Port Addressing
Any memory operand addressing modes can be used to access an I/O port if the port is memory-
mapped. String instructions can also be used to transfer data to memory-mapped ports with an
appropriate hardware interface.
Two addressing modes can be used to access ports located in the I/O space (see Figure 2-22). For
direct I/O port addressing, the port number is an 8-bit immediate operand. This allows fixed ac-
cess to ports numbered 0 to 255. Indirect I/O port addressing is similar to register indirect address-
ing of memory operands. The DX register contains the port number, which can range from 0 to
65,535. Adjusting the contents of the DX register allows one instruction to access any port in the
I/O space. A group of adjacent ports can be accessed using a simple software loop that adjusts the
value of the DX register.
Figure 2-22. I/O Port Addressing
Opcode
SI
DI
Source EA
Destination EA
A1025-0A
Opcode
Data
Port Address
Opcode
Port Address
DX
Direct Port
Addressing
Indirect Port
Addressing
A1026-0A
Summary of Contents for 80C186XL
Page 1: ...80C186XL 80C188XL Microprocessor User s Manual...
Page 2: ...80C186XL 80C188XL Microprocessor User s Manual 1995...
Page 18: ...1 Introduction...
Page 19: ......
Page 27: ......
Page 28: ...2 Overview of the 80C186 Family Architecture...
Page 29: ......
Page 79: ......
Page 80: ...3 Bus Interface Unit...
Page 81: ......
Page 127: ......
Page 128: ...4 Peripheral Control Block...
Page 129: ......
Page 137: ......
Page 138: ...5 ClockGenerationand Power Management...
Page 139: ......
Page 154: ...6 Chip Select Unit...
Page 155: ......
Page 178: ...7 Refresh Control Unit...
Page 179: ......
Page 193: ......
Page 194: ...8 Interrupt Control Unit...
Page 195: ......
Page 227: ......
Page 228: ...9 Timer Counter Unit...
Page 229: ......
Page 253: ......
Page 254: ...10 Direct Memory Access Unit...
Page 255: ......
Page 283: ......
Page 284: ...11 Math Coprocessing...
Page 285: ......
Page 302: ...12 ONCE Mode...
Page 303: ......
Page 306: ...A 80C186 Instruction Set Additions and Extensions...
Page 307: ......
Page 318: ...B Input Synchronization...
Page 319: ......
Page 322: ...C Instruction Set Descriptions...
Page 323: ......
Page 371: ......
Page 372: ...D Instruction Set Opcodes and Clock Cycles...
Page 373: ......
Page 396: ...Index...
Page 397: ......