Real Address Mode
In this mode physical memory is a contiguous array of up to 1 MB. The
selector portion of the pointer is interpreted as the upper 16 bits of a
20-bit address. The remaining four bits are set to zero. This mode of
operation is compatible with the 8088 and the 8086.
Segments in this mode are 64KB in size and may be read, written or
executed. An interrupt may occur if data operands or instructions
attempt to wrap around the end of a segment not using the full 64KB.
The unused end of the segment may be overlaid by another segment
to reduce physical memory requirements.
System Timers
The system has three programmable timer/counters controlled by the
Intel 8254-2 chip. These are channels 0 through 2 defined as follows:
Channel 0
GATE 0
CLK IN 0
CLK OUT 0
Table 6-5: Channel 0
System Timer
TIED ON
1.190MHz OSC
8259A IRQ 0
Channel 1
Refresh Request Generator
GATE 1
TIED ON
CLK IN 1
CLK OUT 1
1 .190MHz OSC
Request Refresh Cycle
Table 6-6: Channel 1
Note: Channel 1 is programmed to generate a 15 microsecond signal.
16
Chapter 6: Appendix
Summary of Contents for Apex 286/12
Page 1: ...TECH 1234 12MHz 286 SYSTEM U ser s Manual ...
Page 15: ...Chapter 1 System Overview ...
Page 38: ...Chapter 2 Setting Up Your System ...
Page 50: ...Figure 2 11 1 5 MB Total Onboard System Memory 12 Chapter 2 Setting Up Your System ...
Page 52: ...Figure 2 14 3MB Total Onboard System Memory 14 Chapter 2 Setting Up Your System ...
Page 53: ...Figure 2 15 4MB Total Onboard System Memory Chapter 2 Setting Up Your System 15 ...
Page 54: ...Figure 2 16 5MB Total Onboard System Memory 16 Chapter 2 Setting Up Your System ...
Page 59: ...Operating Your System ...
Page 78: ...Chapter 4 Keyboard ...
Page 88: ...Troubleshooting ...
Page 96: ...Appendix ...
Page 121: ...Glossary ...