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MEMO1010.TXT
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1992-12-02
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╔═════════════════════════════════════════════════════════════════════════╗
║ ║
║ ISA Bus: Above Board Technical Information ║
║ ║
╚═════════════════════════════════════════════════════════════════════════╝
PARALLEL PORT
PARALLEL PORTS
DOS assigns the names LPT1, LPT2, and LPT3 to parallel ports according to
the number of parallel ports in the computer and the I/O address each
uses. You can have up to three parallel ports in your computer only if
LPT1 is on the IBM Monochrome display Adapter or its equivalent.
Otherwise DOS limits your computer to two parallel ports (LPT1 and LPT2).
When you turn on or restart your computer, DOS checks for parallel ports
first at I/O address 3BC, then at 378, and finally at 278. The first port
it finds becomes LPT1, the second LPT2, and the third LPT3. The SETBOARD
program lets you name the Above Board's port.
You can't set the Above Board port to I/O address 3BC. This address is
reserved for video boards that contain a parallel port.
If you have only one parallel port in the computer, DOS always names it
LPT1, regardless of the I/O address it uses. If you have two parallel
ports, DOS assigns LPT1 to the port using the highest address.
SERIAL PORT GENERAL NOTES
The AB uses the standard IBM AT 9-pin serial connector. Other 9-pin
connectors will not work.
Our serial port will not work in the current loop mode.
DOS Versions through 3.2 support COM1 and COM2 only. DOS 3.3 supports
COM3 and COM4 only on machines whose BIOS can detect the 3rd and 4th
serial ports. (So far, only IBM PS-2 Models 50, 60 & 80 can do this).
Should set COM1 at 3F8 and COM2 at 2F8 unless customer has special
communications software that can recognize serial ports at 3E8 and 2E8.
The AB serial port uses the Intel 82510 chip. The IBM Advanced diagnostics
is looking for an older serial port chip so the AB Serial Port will fail
the IBM Advanced Diagnostics. The only way to test the port is to use a
serial device such as a mouse or modem on it.
SERIAL PORT & INTERRUPTS
┌────────────────────┬───────────────────────────┐
│ Above Board │ Interrupts │
│ Serial Port │ │
╞════════════════════╪═══════════════════════════╡
│ COM 1 (3F8) │ IRQ 4 │
│ COM 2 (2F8) │ IRQ 3 │
│ COM 3 (3E8) │ IRQ 2 or IRQ 5 │
│ COM 4 (2E8) │ IRQ 5 or IRQ 2 │
└────────────────────┴───────────────────────────┘
In Classic bus computers, there is no set convention for choosing the
interrupt for COM3 and COM4.
ACCESS TIMES FOR THE AB 286, AB PLUS, & PLUS 8
8088- and 8086-based computers
┌────────────────┬──────────────┬───────────────┬────────────────┐
│ Frequency │ Bus Clock │ Memory │ I/O │
│ │ Period │ Cycle time │ Cycle Time │
├────────────────┼──────────────┼───────────────┼────────────────┤
│ 4.77 MHz │ 210 ns │ 840 ns │ 1050 ns │
│ │ │ │ │
│ 8.0 MHz │ 125 ns │ 500 ns │ 625 ns │
│ │ │ │ │
│ 10.0 MHz │ 100 ns │ 400 ns │ 500 ns │
└────────────────┴──────────────┴───────────────┴────────────────┘
80286- and 80386-based computers
┌──────────────┬───────┬───────┬────────────────┬─────────┐
│ Memory Range│ 6 MHz │ 8 Mhz │ 10 Mhz │ 12.5 Mhz│
│ accessed │ │ │ 120ns 150ns │ │
╞══════════════╪═══════╪═══════╪═══════╤════════╪═════════╡
│ Conventional │ │ │ │ │ │
│ and Extended │ │ │ │ │ │
│ 16 => 16 │ 501ns │ 375ns │ 300ns │ 400ns │ 334ns │
│ │ 1ws │ 1ws │ 1ws │ 2ws │ 2ws │
╞══════════════╪═══════╪═══════╪═══════╪════════╪═════════╡
│ Expanded │ │ │ │ │ │
│ 8 => 8 │ N/A │ N/A │ 600ns │ 600ns │ 501ns │
│ │ │ │ 4ws │ 4ws │ 4ws │
├──────────────┼───────┼───────┼───────┼────────┼─────────┤
│ 16 => 8 │ N/A │ N/A │1200ns │1200ns │ 1002ns │
│ │ │ │ 10ws │ 10ws │ 10ws │
├──────────────┼───────┼───────┼───────┼────────┼─────────┤
│ 16 => 16 │ 501ns │ 375ns │ N/A │ N/A │ N/A │
│ │ │ 1ws │ │ │ │
└──────────────┴───────┴───────┴───────┴────────┴─────────┴
ws = wait states
8 => 8 8-bit bus operations to 8-bit devices. This takes sixty
clock cycles, including four wait states (generated by the system
board).
16 => 8 16-bit bus operations to 8-bit devices. Takes 12 clock
cycles, including 10 wait states (generated by the system board).
16 => 16 16-bit bus operations to 16-bit devices. Takes three
clock cycles including one wait state (generated by the system
board).
BYTE SWAPPING, MEMCS16, & AB 286
The Above Board 286, Plus, and Plus 8 work in computers with bus speeds of
6, 8, 10, and 12.5 MHz. Use the SETBOARD program to configure the Above
Board for the proper speed. For the Above Board to work correctly, the
computer must add at least one wait state to every memory access on the
bus.
Many computers eliminate wait states for accesses to system board memory,
but these computers still add a wait state to access non-system board
memory. IBM AT computers require this. Computers which do not add the
wait state are not fully IBM AT compatible. Here's how the Above Board
handles wait states for the different bus speeds:
6 and 8 MHz:
MemCS16- works normally, (open-collector), 120ns for extended and
conventional memory. In the C0000 and 150ns RAM D0000 segments,
(expanded memory range), MemCS16- is actively driven hi or lo. It
is driven hi if the bus address is not within the 64Kb page frame
and it is driven lo if the address is within the page frame. The
result of this is that the Above Board can be the ONLY 16-bit
board in the C0000 thru D0000 segments, (UNLESS the 16BIT=xx
parameter is included on the EMM.SYS device driver line). All
other 8-bit boards will work correctly.
10 MHz, 120ns RAM:
MemCS16- works normally (open-collector) for extended and
conventional memory. In the C0000 and D0000 segments MemCS16- is
left in the high-impedance state. This forces the motherboard to
break 16-bit accesses into two 8-bit accesses, (each 8-bit access
contains four wait states as the motherboard default), and the
board reconstructs the data. We call this type of operation a
byte-swap. No extra Wait states are added by the Above Board.
10 MHz, 150ns RAM:
Same as above except that an extra wait state is added for all
extended and conventional memory accesses. If the system is IBM
compatible, the motherboard always inserts one wait state, so our
extra wait state is actually the second. If people have "Zero-
Wait State" machines, determine if the bus has the required wait
state or if the bus is actually zero wait states. Our board
requires at least one from the bus. No MemCS16- remains in high
impedance state in the C0000 and D0000 segments.
12.5 MHz, both RAM speeds:
An extra wait state is added for all extended and conventional
memory accesses. Expanded memory is byte-swapped as described
above. No MemCS16- remains in high impedance state in the C0000
and D0000 segments.
NOTE: PC/XT systems do not use MemCS16 and therefore the Above Board
286 will keep the MemCS16 signal in high impedance for all
above system types where applicable, (4.77 or 8MHz).
EEPROM - HOW MANY TIMES CAN IT BE PROGRAMMED?
The EEPROM on the Above Board is specified for 10,000 erase/write cycles
per
register.
══════════════════════════════════════════════════════════════════════════════
End of file Intel FaxBack # 1010 December 2,1992