C. I/O MAP
IBM PC computer mapped its I/O by used address decoder. There are 400 Hex I/O address locations preserved. Some have been used for its own purpose and some used by the external cards and some are still not been use yet. Tabel A-1. show some of these I/O address used for. In fact, I/O address locations can be as much as 220 locations. But in the previous design it is not used all the address lines. Only 10 lines were used, i.e.: 210 = 1024 locations (400 Hex). If you run out these locations all, there is still way to get some of the locations by used the decoder techniques or by used indexed I/O map. This will be describe later.
The first decision that has to be made when designing a PC prototype card is just where in the input/output map it should be placed. As explained previously, only 1024 of the 65536 possible places for input/output addresses are availabel on a PC, and the lower 512 addresses are reserved for the computer's internal hardware. Much of the upper block of 512 addresses are reserved for essential and standard expansion cards such as serial ports, and display adapters. We can only use the upper block of 512 addresses for our add-ons cards. There are still more places as mark by reserved that are not been used yet by any cards. We can use it. Even the prototype card has the location itself, it can't make a guarantee that these location are still reserved for our purpose, because many company had built their own card that used this location (include one that introduce by the IBM). Besides the standard card, there are many cards was introduced in the market this day, like video card (VCD or DVD card), TV card, radio card, etc ... etc. This also have several I/O locations that can be choose when installed in the first time. Be sure to check your configuration of I/O ports.
D. MEMORY MAP
In the first PC design of memory architecture, memories implemented to it's limit 1 MB boundary (220 as the address only 20 address lines). But not all of this location filled with memories. 216 location (640 kB) was fillled by RAM (Random Access Memory) for the system, program and temporary data. The upper portion was filled with ROM (Read Only Memory) by parts, depends of the configuration of the system; system initialization program, POST (Power On Self Test), BIOS (Basic Input/Output System), BASIC system, display controller, hard disk controller, etc ... etc. This upper portion location also called the UMB (Upper Memory Block) area. If we used DOS version 4.00 and up, we can activated this UMB area to store some portion of the system by put the 'DOS=UMB' statement in the CONFIG.SYS file. But the EMM386.EXE file must be installed first. This ability also valid for any other program if we use the 'LOADHIGH= . . .' statement.
Then the PC design architecture was developing the ability to expanded memory. This technique was development by Lotus-Intel-Microsoft, so become the standard EMS (Expanded Memory Specification) and also called LIM-EMS standard. The alocation method used UMB to map the expanded memory. 16 kB each block and called memory page. Up to 4 pages can be accesses at a time. We can used this option (or any programs which used this standard) by installed EMM386.EXE in the CONFIG.SYS file.
When the AT architecture was introduced, the limit of memory to implemented becomes more wide; 80286 CPU could be implemented up to 16 MB location (24 address lines) and 80386 CPU up to 4 GB (32 address lines). But because of the old design of DOS system, only 1 MB (20 address lines) can be accesses by DOS (DOS run in real mode). To accesses the upper 1 MB, DOS must run in protected mode. These upper 1 MB memory are called XMS (Extended Memory Specification) and can be accesses if we installed EMM386.EXE in the CONFIG.SYS file too, or in the new system like windows system, it was used a DOS Extender program; DPMI, VCPM, etc ... etc. The first 64 kB memory location upper 1 MB memory also called HMA (High Memory Area). This location only for store the data not to execute the program. DOS also kept its data in it by the 'DOS=HI' statement. But the 'HIMEM.SYS' file must be installed first in the CONFIG.SYS file.
Fig. D-1. shows the memory map for the AT computer system. Its also included, memory location used by any programs and drivers, so we could see the whole system by hardware and software.
E. HARDWARE INTERRUPT
In the earlier PC design, only 1 PIC (Programmable Interrupt Controller) implemented, and in the new design, it was added 1 more (cascade). These hardware interrupts have the priority level. Tabel. E-1. shows the complete hardware interrupts and their priority level in PC system design.
F. INTERRUPT VECTOR TABLE (IVT)
IVT is a table locate at 00000 hex. This table has 400 hex length. This table implemented on the Intel design architecture. In the begining, this location is to be used for the processor purpose, but in the PC design architecture the purpose is expanded. It's consist of a pair of pointer location; i.e.: CS:IP; where CS for code Segment and IP for Index Pointer. The size is 16 bit each. This pair of location consist of the routine program to do some task. The related function in the program is, location 00000 ~ 00003 hex used for INT 0, location 00004 ~ 00007 hex used for INT 1, and so on. The task for each interrupt is listed in Tabel. F-1. This table also a combined between hardware interrupt and software interrupt. We can also modified this interrupt to do some task for our purpose just by changing the interrupt pointer location not the whole routine.
IBM PC computer mapped its I/O by used address decoder. There are 400 Hex I/O address locations preserved. Some have been used for its own purpose and some used by the external cards and some are still not been use yet. Tabel A-1. show some of these I/O address used for. In fact, I/O address locations can be as much as 220 locations. But in the previous design it is not used all the address lines. Only 10 lines were used, i.e.: 210 = 1024 locations (400 Hex). If you run out these locations all, there is still way to get some of the locations by used the decoder techniques or by used indexed I/O map. This will be describe later.
| ADDRESS | DEVICE | |
|---|---|---|
| 000H ~ 01FH | DMA Controller 1, 8237A-5 | |
| 020H ~ 03FH | Interrupt Controller 1, 8259A, Master | |
| 040H ~ 05FH | Timer, 8254-2 | |
| 060H ~ 06FH | Keyboard Controller, 8254 | |
| 070H ~ 07FH | Real Time Clock, NMI (Non Maskable Interrupt) Mask | |
| 080H ~ 09FH | DMA (Direct Memory access) page register, 74LS612 | |
| 0A0H ~ 0BFH | Interrupt Controller 2, 8259A | |
| 0C0H ~ 0DFH | DMA Controller 2, 8237A-5 | |
| 0F0H | Clear Math Co-Processor busy | |
| 0F1H | Reset Math Co-Processor | |
| 0F8H ~ 0FFH | Math Co-Processor | |
| 1F0H ~ 1F8H | Fixed Disk Controller | |
| 200H ~ 207H | Game I/O Controller | |
| 210H ~ 217H | Expansion Slot | |
| 220H ~ 24FH | Reserved | |
| 278H ~ 27FH | Parallel Printer Port 3 (LPT-3) | |
| 2E8H ~ 2EFH | Serial Port 4 (COM-4) | |
| 2F0H ~ 2F7H | Reserved | |
| 2F8H ~ 2FFH | Serial Port 2 (COM-2) | |
| 300H ~ 31FH | Prototype Card | |
| 320H ~ 32FH | Fixed Disk Controller | |
| 360H ~ 36FH | Reserved | |
| 378H ~ 37FH | Parallel Printer Port 2 (LPT-2) | |
| 380H ~ 38FH | SDLC, Bisynchronous 2 | |
| 3A0H ~ 3AFH | Bisynchronous 1 | |
| 3B0H ~ 3BBH | Monochrome Display Adapter | |
| 3BCH ~ 3BFH | Parallel Printer Port 1 (LPT-1) | |
| 3C0H ~ 3CFH | EGA/VGA Adapter Controller | |
| 3D0H ~ 3DFH | Color/Graphics Monitor Adapter (CGA Adapter) | |
| 3E8H ~ 3EFH | Serial Port 3 (COM-3) | |
| 3F0H ~ 3F7H | Floppy Disk (Diskette) Controller | |
| 3F8H ~ 3FFH | Serial Port 1 (COM-1) |
The first decision that has to be made when designing a PC prototype card is just where in the input/output map it should be placed. As explained previously, only 1024 of the 65536 possible places for input/output addresses are availabel on a PC, and the lower 512 addresses are reserved for the computer's internal hardware. Much of the upper block of 512 addresses are reserved for essential and standard expansion cards such as serial ports, and display adapters. We can only use the upper block of 512 addresses for our add-ons cards. There are still more places as mark by reserved that are not been used yet by any cards. We can use it. Even the prototype card has the location itself, it can't make a guarantee that these location are still reserved for our purpose, because many company had built their own card that used this location (include one that introduce by the IBM). Besides the standard card, there are many cards was introduced in the market this day, like video card (VCD or DVD card), TV card, radio card, etc ... etc. This also have several I/O locations that can be choose when installed in the first time. Be sure to check your configuration of I/O ports.
D. MEMORY MAP
In the first PC design of memory architecture, memories implemented to it's limit 1 MB boundary (220 as the address only 20 address lines). But not all of this location filled with memories. 216 location (640 kB) was fillled by RAM (Random Access Memory) for the system, program and temporary data. The upper portion was filled with ROM (Read Only Memory) by parts, depends of the configuration of the system; system initialization program, POST (Power On Self Test), BIOS (Basic Input/Output System), BASIC system, display controller, hard disk controller, etc ... etc. This upper portion location also called the UMB (Upper Memory Block) area. If we used DOS version 4.00 and up, we can activated this UMB area to store some portion of the system by put the 'DOS=UMB' statement in the CONFIG.SYS file. But the EMM386.EXE file must be installed first. This ability also valid for any other program if we use the 'LOADHIGH= . . .' statement.
Then the PC design architecture was developing the ability to expanded memory. This technique was development by Lotus-Intel-Microsoft, so become the standard EMS (Expanded Memory Specification) and also called LIM-EMS standard. The alocation method used UMB to map the expanded memory. 16 kB each block and called memory page. Up to 4 pages can be accesses at a time. We can used this option (or any programs which used this standard) by installed EMM386.EXE in the CONFIG.SYS file.
When the AT architecture was introduced, the limit of memory to implemented becomes more wide; 80286 CPU could be implemented up to 16 MB location (24 address lines) and 80386 CPU up to 4 GB (32 address lines). But because of the old design of DOS system, only 1 MB (20 address lines) can be accesses by DOS (DOS run in real mode). To accesses the upper 1 MB, DOS must run in protected mode. These upper 1 MB memory are called XMS (Extended Memory Specification) and can be accesses if we installed EMM386.EXE in the CONFIG.SYS file too, or in the new system like windows system, it was used a DOS Extender program; DPMI, VCPM, etc ... etc. The first 64 kB memory location upper 1 MB memory also called HMA (High Memory Area). This location only for store the data not to execute the program. DOS also kept its data in it by the 'DOS=HI' statement. But the 'HIMEM.SYS' file must be installed first in the CONFIG.SYS file.
Fig. D-1. shows the memory map for the AT computer system. Its also included, memory location used by any programs and drivers, so we could see the whole system by hardware and software.
 | |||
| Fig. D-1. Memory Map of PC/XT/AT computer system. |
In the earlier PC design, only 1 PIC (Programmable Interrupt Controller) implemented, and in the new design, it was added 1 more (cascade). These hardware interrupts have the priority level. Tabel. E-1. shows the complete hardware interrupts and their priority level in PC system design.
| ||||
| IRQ 0 | Timer Int. (8253 PIT channel 0) | INT 08H | ||
| IRQ 1 | Keyboard Int. | INT 09H | ||
| IRQ 2 | Reserved (cascade), Clock Int. | Slave PIC (see below) | INT 0AH | |
| IRQ 3 | Serial Port 2 (COM-2) | INT 0BH | ||
| IRQ 4 | Serial Port 1 (COM-1) | INT 0CH | ||
| IRQ 5 | Fixed Disk Controller Int. | INT 0DH | ||
| IRQ 6 | Floppy Disk Controller Int. | INT 0EH | ||
| IRQ 7 | Parallel Printer Port Int. | INT 0FH | ||
| IRQ 8 | Real Time Clock | INT 70H | | |
| IRQ 9 | Software Redirect to IRQ2 | INT 71H | ||
| IRQ 10 | Reserved | INT 72H | ||
| IRQ 11 | Reserved | INT 73H | ||
| IRQ 12 | Reserved | INT 74H | ||
| IRQ 13 | Coprocessor | INT 75H | ||
| IRQ 14 | Fixed Disk Controller | INT 76H | ||
| IRQ 15 | Reserved | INT 77H |
F. INTERRUPT VECTOR TABLE (IVT)
IVT is a table locate at 00000 hex. This table has 400 hex length. This table implemented on the Intel design architecture. In the begining, this location is to be used for the processor purpose, but in the PC design architecture the purpose is expanded. It's consist of a pair of pointer location; i.e.: CS:IP; where CS for code Segment and IP for Index Pointer. The size is 16 bit each. This pair of location consist of the routine program to do some task. The related function in the program is, location 00000 ~ 00003 hex used for INT 0, location 00004 ~ 00007 hex used for INT 1, and so on. The task for each interrupt is listed in Tabel. F-1. This table also a combined between hardware interrupt and software interrupt. We can also modified this interrupt to do some task for our purpose just by changing the interrupt pointer location not the whole routine.
| INT 30 H ~ INT 3F H | Reserved | ||
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