The RTN key does a return from a subroutine. It also stops a main program and, if nothing’s running at all, it will take you to the “top of memory marker” (“00 00” in w/prgm mode).
Here’s how it does all that: Continue reading HP-65 RTN
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HP-65 – Pressing the [A] key
When you press the [A] key the HP-65 calculator starts looking for a “LBL A” in program memory and then runs it. Unlike the HP-67 which has a “(use) default functions” flag, the HP-65 fires up with its default functions entered into program memory. This simplifies the ’65 processing for [A].
Here’s what happens: Continue reading HP-65 – Pressing the [A] key
HP-65 – The s8 “Running” Flag
It looks like s8 controls whether a program runs or not. Here’s why: Continue reading HP-65 – The s8 “Running” Flag
HP-65 Display X in FIXed mode
Here’s how we get X displayed when we’re in FIXed display mode. Continue reading HP-65 Display X in FIXed mode
HP-65 Key Press Routine
Here’s how we get from a key press to the HP-65 (or emulator) actually doing something … Continue reading HP-65 Key Press Routine
HP-65 Microcode – STO and RCL
Interestingly, all of the STO and RCL instructions in program memory goto the same microcode address. Also of interest is these instructions show the clash between “merged” keystrokes and unmerged ones: STO and RCL are merged keycodes (one step for two key presses); but not all of them are merged. (I think they ran out of available codes before they ran out of key sequences and decided to keep what they could.) As a result, you can see the behaviour of both approaches in the same instruction. Continue reading HP-65 Microcode – STO and RCL
HP-65 Program Code Jump Table
When the HP-65 runs program steps it gets a program code (0-63) from program memory and then does something depending on the program code. Continue reading HP-65 Program Code Jump Table
HP-65 Display Program Step
How does the HP-65 display a program step? If you run the HP-65 emulator with logging turned on and flick the switch to W/PRGM you’ll see. Here’s the details: Continue reading HP-65 Display Program Step
HP-67 Program – Binary View by Class’67
Here’s a program from a contributor, Class’67. It does high precision base conversions. In his words: Continue reading HP-67 Program – Binary View by Class’67
HP65 s3 – W/PRGM
The HP-65 calculator has an internal set of status flags known as the “s register”. “s3” is one of those flags but it behaves a bit strangely … Continue reading HP65 s3 – W/PRGM
HP65 s5 – Memory Full
s5 is used to record “memory full”. Here’s an example: Continue reading HP65 s5 – Memory Full
The HP65 Wait Loop
When the HP-65 calculator is sitting idle, waiting for you to get it to do something, what is it thinking? What’s going through its head? Continue reading The HP65 Wait Loop
The HP65 M Register
The M register in the HP-65 is used for a lot of very interesting things. Maybe not quite “give me the contents of the M register and I’ll show you the world”; but it is very close to that. Continue reading The HP65 M Register
The HP65 Buffer
There is a variable in the HP65 emulator named simply “buffer”. What is it? What does it do? Why is it there? Continue reading The HP65 Buffer
HP65 Flags
The HP-65 calculator has two flags and you can set, clear or test these in your programs. They allow you to remember choices or situations for later. Something happens. You use f SF 1 (or f SF 2) to remember it, and later you use f TF 1 (or f TF 2) to choose between two different courses of action.
Where are the flags stored? How does it do all that? Continue reading HP65 Flags
HP67 – h SF 4 and h CF 4
There are two unused codes in the HP-67 calculator that actually do things. These are “h SF 4” and “h CF 4”. Now, if you know the HP-67 calculator, you know it doesn’t have a “flag 4”. There are only flags 0-3 and you can set, test and clear these to your heart’s content. What’s flag 4? Continue reading HP67 – h SF 4 and h CF 4
HP67 – The Other h PI
There is an unused code for the HP-67 calculator that displays as “h PI”. (It comes up as keycode “35 73”.) It is one of the six codes that you can’t normally enter into the calculator. What does it do? Does it key in PI, like the real one? Does it do something more interesting? Continue reading HP67 – The Other h PI
HP67 – f LBL (i)
The “f LBL (i)” instruction is one of the missing codes that you can’t normally key into a HP-67 calculator. But if you do, what happens? Continue reading HP67 – f LBL (i)
HP67 Microcode – DSP 0
As you probably know, DSP n where n is one of the digit keys [0] to [9] sets the display precision. E.g. DSP 2 in FIXed mode gives you “0.00”, DSP 3 gives “0.000”.
Here’s how the internals do that Continue reading HP67 Microcode – DSP 0
HP67 Merged Keycodes – State Info
As you key in a merged keycode the calculator has to remember which keys led up to this point. After all, pressing the [0] key produces very different results if it was preceded by [f], [g], [h], [STO], [RCL], [STO] [+], and so on. Here’s how it keeps track: Continue reading HP67 Merged Keycodes – State Info
