Below, I show the segment as 'xxxx'.  That is because the segment that DEBUG.COM uses varies.  If I was to show the segment that I saw, some people would worry because the segment displayed to them was different.


Boot from a DOS boot disk that contains DEBUG.COM

Execute DEBUG.  DEBUG will present a dash ("-") prompt.  When you see that prompt, enter the following commands (shown in brown):

- A 100
xxxx:0100 MOV AL,0
xxxx:0102 MOV DX,300
xxxx:0105 OUT DX,AL
xxxx:0106 MOV DX,310
xxxx:0109 OUT DX,AL
xxxx:010A JMP 102
xxxx:010C                <----- at this line just press the [ENTER] key - this will return DEBUG's dash prompt
- g=100


Now, with either a logic probe or oscilloscope:

1. Expect to observe pulses on pin 19 of the U3 chip.   <--- No point in proceeding if these pulses are not present
2. Expect to observe pulses on pin 3 of the U4 chip.
3. Expect to observe pulses on pin 6 of the U4 chip.
4. Expect to observe pulses on pin 7 of the CF connector.
5. Expect to observe pulses on pin 32 of the CF connector.


BTW.  The LED on my XT-CF-Lite card does not turn on during this test.  (The CF card decides when to light the LED.)