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Ruuds Diagnostic ROM  -  Breakdown  -  Versions 4.3 through 4.8


Below, when a 'Checkpoint' is indicated as going to "[LPT1-3]", that means I/O addresses/ports 378h, 278h, and 3BCh.  Those ports are parallel (printer) ports.  If you have a parallel (printer) port at either of those ports, then the device shown at here can be used to view bytes sent to the port.  You can use a parallel printer if it has a 'hex' mode - example at here.

Below, when a 'Checkpoint' is indicated as going to "[COM1]", that means I/O address/port 3F8h.  The first serial port in a computer is usually set to I/O address/port 3F8h.  More information about checkpoints going to COM1 is at here.

Below, when a 'Checkpoint' is indicated as going to "[IBMDIAG]", that means I/O port 80h.  On IBM 5170's, port 80h is used for diagnostic purposes, with an ISA POST card being used to show diagnostic bytes sent to port 80h.  However, on an IBM 5150 or 5160, rarely does an ISA POST card work.  Do not be surprised if it does not work.  More information about that is at here.

A more detailed description of the tests is at here.

For version 4.8

STEP	Video enabled ?	ACTION	IF ERROR	COMMENT
1	No	Within the CPU, disable maskable interrupts, and set the direction flag to increment.
2	No	Disable MDA video, and set the high-resolution bit.		Setting the high-resolution bit at this time, is critical for the IBM made MDA card, the 'IBM Monochrome Display and Printer Adapter'.  Refer to page 5 of the IBM document at here.
3	No	Send checkpoint 33  to [LPT1-3]+[IBMDIAG]		33h chosen because it is very distinctive.  See note 1 below.
4	No	If a serial port at I/O port 3F8h ('COM1') exists: 1. Initialise it to: 9600 baud, no parity, 8 data bits, 1 stop bit. (9600,N,8,1); 2. Then, send '33'.		An ASCII serial terminal, or terminal program, will see: 33     (screen shot)
5	No	Send checkpoint 00  to [LPT1-3]+[COM1]+[IBMDIAG]
6	No	Initialise the MDA/CGA card to 80x25 character mode.		Both MDA and CGA done.  If neither card is present, this step will not fail.
7	Yes	Send checkpoint 01  to [LPT1-3]+[COM1]+[IBMDIAG]
8	Yes	For MDA/CGA, make the cursor invisible.		Both MDA and CGA done.  If neither card is present, this step will not fail.
9	Yes	Send checkpoint 02  to [LPT1-3]+[COM1]+[IBMDIAG]
10	Yes	Clear the MDA/CGA video screen.		Both MDA and CGA done.  If neither card is present, this step will not fail.
11	Yes	Send checkpoint 03  to [LPT1-3]+[COM1]+[IBMDIAG]
12	Yes	On-screen, display the name of the program and the version.		Done for MDA and CGA.
13	Yes	Send checkpoint 04  to [LPT1-3]+[COM1]+[IBMDIAG]
14	Yes	Just in case, disable NMI interrupts.		A good motherboard will automatically do that at power-on time, via hardware.
15	Yes	Send checkpoint 06  to [LPT1-3]+[COM1]+[IBMDIAG]
16	Yes	Initialise the 8255 chip.		Also disables turbo mode for compatible motherboards.
17	Yes	Send checkpoint 08  to [LPT1-3]+[COM1]+[IBMDIAG]
18	Yes	Set up 'unexpected NMI' handler.		See note 2 below.
19	Yes	Send checkpoint 09  to [LPT1-3]+[COM1]+[IBMDIAG]
20	Yes	• Beep the speaker three times: short-long-short. • On the IBM 5150, single-click the relay.		Short-long-short beeping chosen because it is very distinctive.  See note 3 below.
21	Yes	Send checkpoint 0A  to [LPT1-3]+[COM1]+[IBMDIAG]
22	Yes	Look for MDA video RAM. If MDA RAM found, send checkpoint 0B." If MDA RAM not found, look for CGA video RAM. If CGA RAM found, send checkpoint 0C." If MDA RAM and CGA RAM not found, look for 4KB of RAM at A0000. If 4KB of RAM at A0000 found, send checkpoint 0D."	If none of those found: 1. Send checkpoint 8A to [LPT1-3]+[COM1]+[IBMDIAG], 2. then halt.
23	Yes	The last 96 bytes of MDA/CGA/A0000 RAM is unused. We will use those bytes for the stack and some variables. Test those 96 bytes.	If an error: 1. Send checkpoint 8D to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display "Test of video RAM failed.", 3. then halt.	Of interest, later, after motherboard RAM is fully tested, some variables will be stored there.
24	Yes	Send checkpoint 0E  to [LPT1-3]+[IBMDIAG]
25	Yes	Clear our variables.		Zero the variables that the diagnostic stores in MDA/CGA/A0000 RAM.
26	Yes	If a serial port at 3F8h (i.e. COM1) exists, set the 'Com1Exists' variable to 1.		That variable will be checked by later code that intends to send bytes to COM1.
		START OF LOOP
27	Yes	Send checkpoint 10 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
28	Yes	Disable maskable interrupts, and set the direction flag to increment.
29	Yes	Display 00 in the top right corner of the screen.
30	Yes	Send checkpoint 12 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
31	Yes	Display "Testing CPU"
32	Yes	Part 1 of CPU test.	If an error: 1. Send checkpoint 92 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then halt.
33	Yes	Send checkpoint 14 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
34	Yes	Part 2 of CPU test.	If an error: 1. Send checkpoint 94 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then halt.
35	Yes	Send checkpoint 16 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
36	Yes	Display "Diagnostic ROM checksum"
37	Yes	See if 8-bit checksum of ROM is 00h.	If not 00h: 1. Send checkpoint 96 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then halt.
38	Yes	Send checkpoint 18 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
39	Yes	Quote: 'Disable the DMA controller'
40	Yes	Send checkpoint 19 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
41	Yes	Quote: 'Disable the speakers and enable timer 2'
42	Yes	Send checkpoint 1A  to [LPT1-3]+[COM1]+[IBMDIAG]
43	Yes	Display "8253 timer channel 0"
44	Yes	Test 8253 timer channel 0.  Mode 2 only.	If an error, send checkpoint 9A to [LPT1-3]+[COM1]+[IBMDIAG]
45	Yes	Send checkpoint 1B  to [LPT1-3]+[COM1]+[IBMDIAG]
46	Yes	Display "8253 timer channel 1"
47	Yes	Test 8253 timer channel 1.  Mode 2 only.	If an error: 1. Send checkpoint 9B to [LPT1-3]+[COM1]+[IBMDIAG], 2. then halt.	Halt beause with a failing timer 1, there won't be any refresh of motherboard and card RAM.  That compromises a later test of that RAM.
48	Yes	Send checkpoint 1C  to [LPT1-3]+[COM1]+[IBMDIAG]
49	Yes	Display "8253 timer channel 2"
50	Yes	Test 8253 timer channel 2.  Mode 2 only.	If an error, send checkpoint 9C to [LPT1-3]+[COM1]+[IBMDIAG]
51	Yes	Send checkpoint 1F  to [LPT1-3]+[COM1]+[IBMDIAG]
52	Yes	Display "8237A DMA controller"
53	Yes	Test the 8237A DMA controller.	If an error: 1. Send checkpoint 9F to [LPT1-3]+[COM1]+[IBMDIAG], 2. then halt.
54	Yes	Send checkpoint 22 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
55	Yes	Configure the 8237 DMA controller		Includes preparing for RAM refresh by appropriately configuring channel 0.
56	Yes	Send checkpoint 24 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
57	Yes	Display "Hot timer 1 check"
58	Yes	Look for a 'hot' timer 1'	If error, send checkpoint A5 to [LPT1-3]+[COM1]+[IBMDIAG]	The DREQ0 pin on the 8237A DMA controller is expected to be LOW.
59	Yes	Send checkpoint 26 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
60	Yes	Initialise channel 1 on the 8253 timer chip.		One pulse per approximately 15 µs.  See here.
61	Yes	Send checkpoint 28 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
62	Yes	Display "RAM parity error latches"
63	Yes	Step 1:  Clear/disable the two 'RAM parity error' latches. Step 2:  Verify that neither of the two latches are showing as set.	If error, send checkpoint A7 to [LPT1-3]+[COM1]+[IBMDIAG]
64	Yes	Send checkpoint 2A  to [LPT1-3]+[COM1]+[IBMDIAG]
65	Yes	Display "Check first 2 KB of RAM"
66	Yes	Check the first 2 KB of RAM.	If an error: 1. Send checkpoint AA (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display error details on-screen, 3. then send error details to [COM1], 4. then halt.	If an error:  An RS-232 serial terminal (or terminal program) on COM1 will see something like 'AA 4000 20'  In the example given, the '4000' is the failing address.  In the example given, the '20' is the bit error pattern.  00 indicates the parity bit.
67	Yes	Send checkpoint 32 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
68	Yes	Display "Found RAM:"
69	Yes	Establish where the top of conventional memory (RAM up to 640 KB) is, but don't display the figure just yet.		Done by starting at address 640 KB, then searching down until RAM is found. NOTE: In the misconfiguration shown at here, the diagnostic will report 640 KB.  Same if a RAM card goes faulty in a way that creates a gap between motherboard RAM and card RAM.
70	Yes	Send checkpoint 34 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
71	Yes	Display the figure established at step 69.
72	Yes	Send checkpoint 35 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
73	Yes	Display "Testing RAM - Data"
74	Yes	Do a data test of the found RAM.	If an error: 1. Send checkpoint B5 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display error details on-screen, 3. then send error details to [COM1], 4. then halt.	If an error:  An RS-232 serial terminal (or terminal program) on COM1 will see something like 'B5 4000 20'  In the example given, the '4000' is the failing address.  In the example given, the '20' is the bit error pattern.  00 indicates the parity bit.
75	Yes	Send checkpoint 37 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
76	Yes	Display "Testing RAM - Address"
77	Yes	Adddress test of the found RAM - Part 1 of 2. See here for a crude description of a memory addressing problem.	If an error: 1. Send checkpoint B7 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display error details on-screen, 3. then send error details to [COM1], 4. then halt.	If an error:  An RS-232 serial terminal (or terminal program) on COM1 will see something like 'B7 4000 20'  In the example given, the '4000' is the failing address.  In the example given, the '20' is the bit error pattern.
78	Yes	Adddress test of the found RAM - Part 2 of 2.	If an error: 1. Send checkpoint B8 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display error details on-screen, 3. then send error details to [COM1], 4. then halt.	If an error:  An RS-232 serial terminal (or terminal program) on COM1 will see something like 'B8 4000 20'  In the example given, the '4000' is the failing address.  In the example given, the '20' is the bit error pattern.
79	Yes	Send checkpoint 39 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
80	Yes	Display "Testing RAM - Refresh"
81	Yes	Do a test of RAM refresh.	If an error: 1. Send checkpoint B9 (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display error details on-screen, 3. then send error details to [COM1], 4. then halt.	90 second delay between test write then read-back.  A 90 second count-down will be seen on the screen.  If an error:  A serial terminal (or terminal program) on COM1 will see something like 'B9 4000'  In the example given, the '4000' is the failing address.
82	Yes	Send checkpoint 3A  to [LPT1-3]+[COM1]+[IBMDIAG]
83	Yes	Display "Testing RAM - Slow Refresh"
84	Yes	Test the RAM at the refresh rate of 2 milliseconds.	If an error: 1. Send checkpoint BA (hex) to [LPT1-3]+[COM1]+[IBMDIAG], 2. then display error details on-screen, 3. then send error details to [COM1], 4. then halt.	If an error:  An RS-232 serial terminal (or terminal program) on COM1 will see something like 'BA 4000 20'  In the example given, the '4000' is the failing address.  In the example given, the '20' is the bit error pattern.
85	Yes	Send checkpoint 3E  to [LPT1-3]+[COM1]+[IBMDIAG]
86	Yes	Display "8259 interrupt controller"
87	Yes	Test the 8259 interrupt controller.	If an error, send checkpoint BE to [LPT1-3]+[COM1]+[IBMDIAG]
88	Yes	Send checkpoint 40 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
89	Yes	Display "Hot IRQ interrupts".
90	Yes	Check if the 8259 sees an interrupt (IRQ0 to IRQ7) when one is unexpected.	If an interrupt, send checkpoint C0.
91	Yes	Send checkpoint 42 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
92	Yes	Display "Checking interrupt IRQ0".
93	Yes	Verify correct operation of Interrupt 0.	If an error, send checkpoint C2 to [LPT1-3]+[COM1]+[IBMDIAG]
94	Yes	Send checkpoint 46 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
95	Yes	Display "Hot NMI".
96	Yes	Verify that the 8088 CPU is not receiving an NMI.	If an error (NMI present), send checkpoint C6 to [LPT1-3]+[COM1]+[IBMDIAG]
97	Yes	Send checkpoint 4E  to [LPT1-3]+[COM1]+[IBMDIAG]
98	Yes	Display "Keyboard responds to reset".
99	Yes	Software reset the keyboard, and see if in response, the keyboard sends the expected byte of AA.	If an error, send checkpoint CE to [LPT1-3]+[COM1]+[IBMDIAG]
100	Yes	Send checkpoint 50 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
101	Yes	Display "Keyboard stuck key".
102	Yes	See if the keyboard is reporting a stuck key.	If an error, send checkpoint D0 to [LPT1-3]+[COM1]+[IBMDIAG]
103	Yes	Send checkpoint 52 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
104	Yes	Display "Check floppy controller".
105	Yes	See if a reset of the floppy controller is successful.	If an error, send checkpoint D2 to [LPT1-3]+[COM1]+[IBMDIAG]
106	Yes	Send checkpoint 54 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
107	Yes	Display "Trying to read a floppy".
108	Yes	Try to read a track on a 360K floppy.	If an error, send checkpoint D4 to [LPT1-3]+[COM1]+[IBMDIAG]	360K floppy drive required.
109	Yes	Send checkpoint 60 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
110	Yes	Display "Check ROM at F4000".		IBM 5150: IC socket U28.   IBM 5160: IC socket U19.   Diagram at here.
111	Yes	Verify that 8 KB at F4000 has an 8-bit checksum of 00. (Ignore result if no 8KB ROM at F4000 - may pass, may fail.)		Ignore result if no 8KB ROM at F4000 - may pass, may fail.
112	Yes	Send checkpoint 61 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
113	Yes	Display "Check ROM at F6000".		IBM 5150: IC socket U29.   IBM 5160: IC socket U19.   Diagram at here.
114	Yes	Verify that 8 KB at F6000 has an 8-bit checksum of 00. (Ignore result if no 8KB ROM at F6000 - may pass, may fail.)		Ignore result if no 8KB ROM at F6000 - may pass, may fail.
115	Yes	Send checkpoint 62 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
116	Yes	Display "Check ROM at F8000".		IBM 5150: IC socket U30.   IBM 5160: IC socket U18.   Diagram at here.
117	Yes	Verify that 8 KB at F8000 has an 8-bit checksum of 00. (Ignore result if no 8KB ROM at F8000 - may pass, may fail.)		Ignore result if no 8KB ROM at F8000 - may pass, may fail.
118	Yes	Send checkpoint 63 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
119	Yes	Display "Check ROM at FA000".		IBM 5150: IC socket U31.   IBM 5160: IC socket U18.   Diagram at here.
120	Yes	Verify that 8 KB at FA000 has an 8-bit checksum of 00. (Ignore result if no 8KB ROM at FA000 - may pass, may fail.)		Ignore result if no 8KB ROM at FA000 - may pass, may fail.
121	Yes	Send checkpoint 64 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
122	Yes	Display "Check ROM at FC000".		IBM 5150: IC socket U32.   IBM 5160: IC socket U18.   Diagram at here.
123	Yes	Verify that 8 KB at FC000 has an 8-bit checksum of 00. (Ignore result if no 8KB ROM at FC000 - may pass, may fail.)		Ignore result if no 8KB ROM at FC000 - may pass, may fail.
124	Yes	Send checkpoint 6A  to [LPT1-3]+[COM1]+[IBMDIAG]
125	Yes	Display the switch setting
126	Yes	Send checkpoint 72 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]
127	Yes	Update the 'Completed passes' figure
128	Yes	Send checkpoint 74 (hex)  to [LPT1-3]+[COM1]+[IBMDIAG]

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Note 1	Possible problems in using 00 instead could be: • 00 might be the default power-on display of some parallel/LPT monitoring devices. • Some parallel/LPT monitoring devices may register a 00 (and other bytes) at power-on time.
Note 2	Low RAM is untested at this point, but do it anyway. In fact, there may be no low RAM at all, but do it anyway. If the 'unxepected NMI' handler gets called, checkpoint 99 will be sent, and *** UNEXPECTED NMI *** be displayed on a MDA/CGA screen.
Note 3	Yes, we are taking the chance that the circuitry involved in beeping the speaker is working. No beeps might be because: • No speaker connected to motherboard. • Diagnostic ROM not created properly. • Diagnostic ROM has started to execute, but circuitry involved in beeping the speaker is faulty.