Decimal Point Format (SPICE series)

[Mike T.]

I recently asked a question about the decimal point format on the SPICE series machines.

Having taken a closer look at the contents of the registers used to generate the display I was wondering if cutting the link on the power supply board actually changes the value of a status register bit (or something else the processor can detect) as the firmware does appear to enable both the decimal point and the comma display segments separately which makes me think that it does play a part somewhere.

Can anyone shed any light on this?

Thanks

[teenix]

The display digit LEDs being on or off are determined by the 4 bit nibbles in Registers A and B, which are decoded inside the CPU IC. These nibbles are sent through the display decoder as each digit is to be displayed and probably latched and then decoded as the next 4 bits enter.

Register A nibbles determine the digit 0 - 9, E, r and o.
Register B nibble determine the digit sign, DP or Comma.

If register B nibble bit 0 = 1, then a DP or Comma should display
If register B nibble bit 1 = 1, then a DP will display
If register B nibble bit 1 = 0, then a Comma will display

The FX pin on the CPU IC is connected to the power supply VCC rail via the link on the power supply board. If the link is in, FX = Logic 1. If the link is out, FX = Logic 0.

if FX = Logic 1, then the DP or Comma display will happen as above.
If FX = Logic 0, then bit 1 of the B nibble will be inverted, changing the DP for a Comma and vice versa.

I guess a simple 2 input XOR gate is connected to bit 1 of the display decoder latch and the FX input.

cheers

Tony

[Mike T.]

This is one of those rabbit holes - I guess that would be easy to test that theory with a self test?

Does any one have a 'european' SPICE series machine that they can use to post a picture of the result of a `STO-ENTER` operation?

Thanks

[Geoff Quickfall]

I have both radix displays on a Spice with the jumper cut and without. Stack is identical as is all other math. As far as the CPU interpretation goes, teenix seems to have nailed it, from what I understand.

You can reverse the jumper cut as HP has by simply applying solder to a cut jumper or by cutting the jumper.


https://www.hpmuseum.org/forum/archive/i...20188.html

Older post with pictures of jumper.

[Mike T.]

Thanks.

If tenix is right (and I suspect he is) then I think that the result of a self test on a 'european' machine should be

-8.8.8.8.8.8.8.8.8.8. (rather then -8,8,8,8,8,8,8,8,8,8,)

However, I'm reluctant to open up any of my calculators and modify the jumper to find out if this is true, but it would be nice if someone could confirm it...

[teenix]

I tested real hardware with the link in and out, the comma is displayed in both modes for [STO] [Enter]

Bit 0 for Register B nibbles are cleared = 0 for the STO Enter -8,8,8,etc display.

I suppose then that the logic is...

If RegB nibble bit 0 = 0, then display Comma regardless of bit 1 and the FX input.
If RegB nibble bit 0 = 1, then display the Comma and DP as explained in previous post.

If there is an XOR gate to determine the US/Euro display, then logically ANDing this output to the display latch bit 0 will produce the correct result.

Thanks Mike, for bringing this up. I didn't think of this and updated my emulator.

cheers

Tony

[rprosperi]

(04-18-2024 06:56 AM)teenix Wrote:  I tested real hardware with the link in and out, the comma is displayed in both modes for [STO] [Enter]

This is the only result that makes sense, since the purpose of this display is to verify that all LED segments on the machine are working. Even if not used by default on machines targeted to markets that use decimal points for the digit separator, the jumper could be cut (e.g. if sold to a person that uses commas) and the full symbols are then required. And I have in fact seen a Spice where the descender portion of the comma had failed, which would not be detected by a display of just decimal points.

[Mike T.]

(04-18-2024 06:56 AM)teenix Wrote:  I tested real hardware with the link in and out, the comma is displayed in both modes for [STO] [Enter]

Thanks