Troubleshooting with a logic probe

A logic probe, such as the TTL Logic Probe is a step up from a voltmeter and give you more insight of what is going on in your RC2014. It does not give as much information as an oscilloscope, but is a lot cheaper and easier to use, and will often point you towards the right area if something isn't working as expected.

A good place to start is to probe each signal on the backplane. Depending on which RC2014 you have, and what is on the ROM you will get different results. Find the system and ROM image below that most closely matches your setup and compare each pin on the backplane. Note that these readings should be taken after power has been applied and after the reset button has been pushed. Remove all expansion modules, just leaving the CPU, ROM, RAM, Serial and Clock.

Any signals shown as high should be high. Any shown as low should be low. Any shown as activity should have some activity, although the variation between high/low duty cycle is only a rough guide, and can be open to interpretation.

Any deviation from these will suggest where you need to focus your attention. For example, if Data D4 is constantly high, refer to the schematic and check the solder joint on each pin on each chip that connects to D4. If the /Reset pin is showing activity and you are not pushing the reset button, check every pin that is connected to the reset line. Of course it is impossible to give an exhaustive list of every possible error, but hopefully you will see something unexpected and know where to look closer.

Microsoft BASIC 4.7 32k

As shipped with RC2014 Micro, RC2014 Micro+, RC2014 Mini, RC2014 Mini II, RC2014 Classic, RC2014 Classic II

Pin	Signal	Value	LED
1	A15	Act (50/50)
2	A14	Low
3	A13	Low
4	A12	Low
5	A11	Low
6	A10	Low
7	A9	Low
8	A8	Low
9	A7	Low
10	A6	Act (mostly High)
11	A5	Act (mostly High)
12	A4	Act (mostly High)
13	A3	Act (50/50)
14	A2	Act (50/50)
15	A1	Act (50/50)
16	A0	Act (50/50)
17	Gnd	Low
18	5V	High
19	M1	Act (mostly High)
20	/Reset	High
21	Clock1	Act (mostly High)
22	/Int	High
23	/MREQ	Act (50/50)
24	/WR	High
25	/RD	Act (50/50)
26	/IORQ	High
27	D0	Act (50/50)
28	D1	Act (50/50)
29	D2	Act (50/50)
30	D3	Act (50/50)
31	D4	Act (50/50)
32	D5	Act (50/50)
33	D6	Act (50/50)
34	D7	Act (50/50)
35	/TX1	High
36	/RX1	High
37
38
39
40

SCM v1.0.0

As shipped with RC2014 Micro, RC2014 Micro+, RC2014 Mini, RC2014 Mini II, RC2014 Classic, RC2014 Classic II, RC2014 Pro

Pin	Signal	Value	LED
1	A15	Act (50/50)
2	A14	Act (50/50)
3	A13	Act (50/50)
4	A12	Act (50/50)
5	A11	Act (50/50)
6	A10	Act (50/50)
7	A9	Act (50/50)
8	A8	Act (50/50)
9	A7	Act (50/50)
10	A6	Act (50/50)
11	A5	Act (50/50)
12	A4	Act (50/50)
13	A3	Act (50/50)
14	A2	Act (50/50)
15	A1	Act (50/50)
16	A0	Act (50/50)
17	Gnd	Low
18	5V	High
19	M1	Act (mostly High)
20	/Reset	High
21	Clock1	Act (mostly High)
22	/Int	High
23	/MREQ	Act (50/50)
24	/WR	Act (mostly High)
25	/RD	Act (50/50)
26	/IORQ	Act (mostly High)
27	D0	Act (50/50)
28	D1	Act (50/50)
29	D2	Act (50/50)
30	D3	Act (50/50)
31	D4	Act (50/50)
32	D5	Act (50/50)
33	D6	Act (50/50)
34	D7	Act (50/50)
35	/TX1	High
36	/RX1	High
37
38
39
40

CP/M BIOS 1.0 G Searle

As supplied with RC2014 Pro, Mini II CP/M Upgrade and Classic II CP/M Upgrade

Pin	Signal	Value	LED
1	A15	Low
2	A14	Act (mostly Low)
3	A13	Low
4	A12	Low
5	A11	Low
6	A10	Low
7	A9	Act (50/50)
8	A8	Act (50/50)
9	A7	Act (50/50)
10	A6	Act (50/50)
11	A5	Act (50/50)
12	A4	Act (50/50)
13	A3	Act (50/50)
14	A2	Act (50/50)
15	A1	Act (50/50)
16	A0	Act (50/50)
17	Gnd	Low
18	5V	High
19	M1	Act (mostly High)
20	/Reset	High
21	Clock1	Act (mostly High)
22	/Int	High
23	/MREQ	Act (mostly High)
24	/WR	Act (mostly High)
25	/RD	Act (50/50)
26	/IORQ	High
27	D0	Act (50/50)
28	D1	Act (50/50)
29	D2	Act (50/50)
30	D3	Act (50/50)
31	D4	Act (50/50)
32	D5	Act (50/50)
33	D6	Act (50/50)
34	D7	Act (50/50)
35	/TX1	High
36	/RX1	High
37
38
39
40
Enhanced Bus
1	Gnd	Low
2	5V	High
3	/RFSH	Act (mostly High)
4	/Page	High
5	Clock2	Act (mostly High)
6	/BUSACK	High
7	/Halt	High
8	/BUSRQ	High
9	/Wait	High
10	/NMI	High
11
12
13
14
15
16
17
18
19	/TX2	High
20	/RX2	High

RomWBW 3.4.0

As supplied with RC2014 Zed and RC2014 Zed Pro

Pin	Signal	Value	LED
1	A15	Act (50/50)
2	A14	Act (50/50)
3	A13	Act (50/50)
4	A12	Act (50/50)
5	A11	Act (50/50)
6	A10	Act (50/50)
7	A9	Act (50/50)
8	A8	Act (50/50)
9	A7	Act (50/50)
10	A6	Act (50/50)
11	A5	Act (50/50)
12	A4	Act (50/50)
13	A3	Act (50/50)
14	A2	Act (50/50)
15	A1	Act (50/50)
16	A0	Act (50/50)
17	Gnd	Low
18	5V	High
19	M1	Act (mostly High)
20	/Reset	High
21	Clock1	Act (mostly High)
22	/Int	High
23	/MREQ	Act (50/50)
24	/WR	Act (mostly High)
25	/RD	Act (50/50)
26	/IORQ	Act (mostly High)
27	D0	Act (50/50)
28	D1	Act (50/50)
29	D2	Act (50/50)
30	D3	Act (50/50)
31	D4	Act (50/50)
32	D5	Act (50/50)
33	D6	Act (50/50)
34	D7	Act (50/50)
35	/TX1	High
36	/RX1	High
37
38
39
40
Enhanced Bus
1	Gnd	Low
2	5V	High
3	/RFSH	Act (mostly High)
4	/Page	Act (mostly High)
5	Clock2	Act (mostly High)
6	/BUSACK	High
7	/Halt	High
8	/BUSRQ	High
9	/Wait	High
10	/NMI	High
11
12
13
14
15
16
17
18
19	/TX2	High
20	/RX2	High

Disclaimer. Whilst every care has been taken to ensure the readings above are correct, it is entirely possible that errors have crept in. If you spot something which you think is wrong, please use the Contact page to let us know and fix any errors.