

>>>>>>>>  TEST5066


--------------------------------------------------
TARGET
--------------------------------------------------

This is code to go into ROM U33 on an IBM 5150 (IBM PC) motherboard.
The IBM 5150 has special ROM requirements. See http://www.minuszerodegrees.net/5150/motherboard/5150_u33.htm


--------------------------------------------------
REQUIRED
--------------------------------------------------

1. A way of putting the BIN file into a suitable ROM/EPROM/EEPROM.
   The IBM 5150 has special ROM requirements. See http://www.minuszerodegrees.net/5150/motherboard/5150_u33.htm

2. Logic analyser (and the knowledge of how to use it).


--------------------------------------------------
BIN FILES
--------------------------------------------------

Per http://www.minuszerodegrees.net/5150/motherboard/5150_u33.htm, if a suitable adapter is used, 16 KB and 32 KB sized ROM/EPROM's can be used on the IBM 5150 motherboard.
Because of that, included here are 16 KB and 32 KB versions of TEST5066_8KB_SIZED.BIN, being TEST5066_16KB_SIZED.BIN and TEST5066_32KB_SIZED.BIN

TEST5066_8KB_SIZED.BIN is for an MCM68766 EPROM, or a 2564 EPROM.
TEST5066_32KB_SIZED.BIN is for a 27C256 EPROM (in a suitable adapter) or W27E257 EEPROM (in a suitable adapter).

Again, see http://www.minuszerodegrees.net/5150/motherboard/5150_u33.htm


--------------------------------------------------
WHAT DOES THE CODE DO ?
--------------------------------------------------

In a loop, the code:
Step 1: Reads address 55555 hex  (5555:0005) (01010101010101010101 binary)
Step 2: Reads address AAAAA hex  (AAAA:000A) (10101010101010101010 binary)

55555 and AAAAA chosen because they will reveal if any adjacent bits are 'shorted'.

An example of adjacent bits is A0 and A1.
An example of adjacent bits is A1 and A2.
An example of adjacent bits is A2 and A3.


--------------------------------------------------
WHAT YOU SHOULD OBSERVE IF USING A LOGIC ANALYSER
--------------------------------------------------

Reference diagram at https://minuszerodegrees.net/5150/misc/5150_address_bus.jpg

Using a logic analyser:
1. On the address bus, verify that two of the addresses seen are 55555 and AAAAA, i.e. all adjacent bits are at different logic states.
2. On the external address bus, verify that two of the addresses seen are 1555 and AAA, i.e. all adjacent bits are at different logic states.

( In the IBM 5150, the external address bus is the lowest 13 bits of the address bus. )


--------------------------------------------------
WHAT YOU SHOULD OBSERVE IF USING AN OSCILLOSCOPE
--------------------------------------------------

Reference diagram at https://minuszerodegrees.net/5150/misc/5150_address_bus.jpg

Using an oscilloscope:
Verify that adjacent bits are at different logic states.

E.g. When you see A4 at HIGH, A3 and A5 should be LOW.


