HP25 scary moments
Message #1 Posted by Vieira, Luiz C. (Brazil) on 8 Jan 2003, 3:49 p.m.
Hi;
yesterday night I was testing a Thevenin (single, real components Eth and Rth equivalency) program in the HP55 and I saw it would work in the HP25, too. As I mentioned before, I cannot keep a calculator without finding something to do with it...
The program is 15 steps long, 55 version, and 13 steps long for the HP25 because it uses one register, and STO 0 / RCL 0 in the HP55 use two steps each.
I loaded it in the HP55 and run it: Rth and Eth returned fine. The problem was with the HP25: ON, PRGM mode and the display insisted on an annoying [nn 13 00] (keycode for [GTO] 00) for each key pressed! "RAM is gone!" I thought. I tested the memories and they returned 0.00 for any value I stored on them. "RAM IS GONE!!!" I cried out loud inside my brain, reverbs and echoes granted.
Soldering iron plugged and lets try with a magnifying lens to find any "cold-soldering" (I learn fast...). None visible, let's go for plan B: heat-up all terminals in both 16- and 18-pin IC's, I would not touch the CPU. (I have one question in the end of this text). I also heat some passive components' terminals close to the same IC's.
Happy end: the HP25's RAM got back to life, I loaded the Thevenin program on it and results were fine. And I got to bed in the down (about 6:00 AM), but I was relieved. Detail: HP25 runs about two times faster than the HP55, at least in this program.
My question is: the HP 25 and the HP25C share the same AMI 1818-0154 chip. Is this the ACT chip? As both have exactly the same instruction and behavior set, I thought this could be ROM. The other two chips, CPU included, have different numbers: the 25 CPU is an MK6215N, ID 1820-1523 while the 25C's CPU is an MK6217N, ID 1820-1741 (as they deal with different RAM structure, they must handle data bus differently); the other chip, supposedly the RAM, is an MK6220N, ID 1820-1564 in the 25, while the HP25C has an HP5061-0469 2.
All of this is because the HP25C with me has an strange behavior: it lits on, accepts number keys and display control, stores and recalls numbers, stores any program keystroke sequence (key numbers are fine) but returns a [0.000000000] for each attempt of anything else, even stack manipulations, [CHS], [.], [EEX] or [CLx]. I think it's a ROM problem, and I would like to confirm if the common AMI 1818-0154 does it, or if this is the ACT chip and the ROM is inside the CPU.
Can anybody point the differences out?
Thank you in advance.
The THEVENIN listing and coments
The Thevenin prgm computes Rth and Vth equivalent for a single Vcc constant-current voltage source with R1 being the series resistance and R2 parallel to load resistance. The procedure is:
Input Press Display
Vcc [ENTER] Vcc
R1 [ENTER] R1
R2 [R/S] Rth
[x<>y] Vth
For testing purposes: suppose you have a 10 Vcc voltage source, R1=5 ohms (series with [+] pole) and R2=10 ohms (parallel with load). What are the values for the equivalent Thevenin Vth and Rth?
Input Press Display
10 [ENTER] 10.00
5 [ENTER] 5.00
10 [R/S] 3.33
[x<>y] 6.67
Solution: Rth=3.33 ohms and Vth=6.67 Vcc
The listing: (keystrokes are for both machines)
HP25 HP55 Keystrokes
[01 21] [ 01 22] x<>y
[02 31] [ 02 41] ENTER^
[03 22] [ 03 23] Rv (roll down)
[04 15 22] [ 04 13] 1/x ([g][1/x] in the HP25)
[05 21] [ 05 22] x<>y
[06 15 22] [ 06 13] 1/x ([g][1/x] in the HP25)
[07 51] [ 07 61] +
[08 15 22] [ 08 13] 1/x ([g][1/x] in the HP25)
[09 23 00] [ 09 33] STO (STO 00 in the HP25)
[ 10 00] 00
[10 61] [ 11 71] ×
[11 21] [ 12 22] x<>y
[12 71] [ 13 81] ÷
[13 24 00] [ 14 24] RCL (RCL 00 in the HP25)
[ 15 00] 00
If you think it's worth, I'll put it in the Programs Library. It works fine in both 11C and 15C too, but their versions do not use registers, just the stack, because they use [R^], not available in the 25 and 55. And in the HP15C it computes complex results, if needed.
Let me know.
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