The HP-65 and HP-67 calculators have the ability to save information onto small magnetic cards. This allows you to save and reload programs so that you don’t need to key them in again each time. With the HP-67 you can also save and reload data that is in the calculator memories.
With the emulators however, Continue reading Saving Magnetic Cards
The hp67u emulator shows a “0.00” before you get a chance to select debugging so how can you explore the HP-67’s startup code?
Continue reading HP67 Startup code
There are six instructions you can’t enter into a HP-67 calculator.
Continue reading HP67 Unused Program Codes
There were a number of strange things you could do with a HP-67 calculator when they first came out and this one stuck in my memory somehow.
As you probably know, there are only 224 program steps in the programmable part of the HP-67. Well, there were some things you could do that would get you to program step 992. Here’s the details:
Continue reading HP67 Program Step 992
With the HP67 we use LBL to name a subroutine, GSB to call one and RTN to return from one.
The question is, “how does the HP-67 know where to return to?” It needs to remember where it is up to. Where does it store that information?
Continue reading HP67 GSB and RTN
The HP67 saves the user program counter in the bottom 3 nibbles (2,1,0) of ram[61]. However, you could be forgiven for thinking that those three digits don’t look anything like the program counter display. Here’s why
Continue reading HP67 User Program Counter
The HP67 internal flags S 9 and S 12 are used during keyboard data entry. The meanings for S9,S12 are: Continue reading HP67 Internals – S 9 and 12
The HP67 calculator has three angle modes: DEG, RAD and GRD.
DEG is degrees. There are 360 degrees in a circle.
RAD is radians. There are 2*PI radians (about 6.28) in a circle.
GRD is gradians. I’d never heard of these before I got my original HP67 but apparently these are used in some fields and there are 400 gradians in a circle.
Continue reading HP67 DEG, RAD and GRD
When you select FIX, SCI or ENG mode in the HP67 it stores 22, 00 or 40 in nibbles 5 & 4 of ram[62]. It works like this:
Continue reading HP67 FIX, SCI and ENG
The HP67 stores PI/4 in ROM subroutine 05043 with 13 digit precision. It multiplies that by 4 (“c + c -> c[w]” twice) to get 3.1415926535900 and then rounds that to 3.141592654.
It works like this:
Continue reading HP67 h PI
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The HP67 calculator has 4 flags. These can be set, cleared or tested. You use them in a user program to remember situations and to behave differently according to the situations. One example might be: the user entered a value (or not) and your program behaves suitably either way. There were a whole stack of programs at the time where you could enter a value and press [A], [B], [C] etc to store the value; or just press the button to calculate it. These included tax calculators, principal and interest calculators and ohms law – key in any two and press the third button for it to work out the third value. Continue reading HP67 Flags
The HP67 Error routine displays “Error”, flashes once (blank out and then comes back) and then waits for a keypress to clear the error message. It works like this Continue reading HP67 Error Routine
This needs more analysis, but here’s what happens when you press [f] [CL PRGM]
Continue reading HP67 f CL PRGM
The HP67 card reader contains two instructions that control a “default functions” flag.
The card reader integrated circuit is a Mostek MK6250N. That connects to the Arithmetic, Control and Timing (ACT) chip and actions a number of instructions that the ACT doesn’t understand. Instructions are 10 bits long. For this article the ones we are interested in are: Continue reading HP67 Card Reader – Default Functions
This is a work in progress and likely to be updated.
The HP67 Arithmetic, Control and Timing chip (ACT) is a Mostek MK6216N. It understands most of the instructions but the HP67 card reader chip (CRC, a Mostek MK6250N) adds instructions and two more data registers: Continue reading HP67 Card Reader
When the HP67 detects that a key has been pressed, it exits the HP67 Keypress Wait Loop and gets to instruction 0214 (octal). Then this happens: Continue reading The HP67 Keypress Routine
Woodstock was the name HP gave to its newer model processor for its newer model calculators at the time of the HP-67, HP-21, HP-25/C and HP-29. Here’s what was in it: Continue reading Woodstock Microcode
This is the microcode in a HP67 calculator that waits for a key press.
00167: 0 -> s 3 00170: CRC 1500 00171: if 1 = s 3 00172: then go to 0263 00173: 0 -> s 1 00174: CRC 300 00175: if 1 = s 3 00176: then go to 0204 00177: if 0 = s 11 00200: then go to 0206 00206: 0 -> s 3 00207: CRC 560 00210: if 1 = s 3 00211: then go to 1324 00212: if 0 = s 15 00213: then go to 0167
It spends most of its time in this loop just checking to see if there is anything to do.
The addresses above are in octal. All of them are < 256 decimal so they are all in rom 0 of the first “quad rom” (one chip with 4 lots of 256 microcode instructions). Roms 0, 1, 2 and 3 are in the first quad.
The CRC instructions are “card reader circuit” commands.
CRC 1500 checks a flag in the card reader and if set, sets the s 3 flag in the calculator (and clears the card reader flag). I don’t know what the flag means yet but 0263 is likely to answer that.
CRC 300 checks the run-w/prgm switch. If you are in “W/PRGM” then it sets the s 3 flag. It clears it if you are in “RUN” mode.
CRC 560 checks whether a card has been inserted into the card reader. If so, s 3 gets set. If not, s 3 is 0.
s 15 gets set when a key has been pressed. This suggests that 00214 onwards deals with a key press.
s 11 is a mystery at present. If does seem to go into code that checks whether MERGE has been selected so it may be card reader related.
The HP65 Emulator has a number of extra functions available. You can access these from the menu and you can get to the menu by tapping the display.
Click here on the emulator.
Then you’ll see the following:
Continue reading The HP65 Emulator Menu
