HP97 The journey begins

[teenix]

Hi all,

Some more progress.

I have the display module mounted and board populated. The original pins have to be used for the display connections and was a bit if a brain teaser to fit them properly. Have to be careful with this display module as it looks the same construction as the Spice which I have seen a few of the LED digits dislodging from the circuit board.

I programmed some simple LED flash code to test the processor and it is working on the CPU board while plugged into the battery board and turned on via the 19C power switch.

Next up, verify the 19C operational code and LED driver routines and see if the LEDs light up. All new circuitry so fingers crossed.

cheers

Tony

[tangdfx]

Hi，Tony

Is it possibile that use only one PCB to replace the original two PCB design.

The bottom PCB only to provide the interface to printer and power source.

[teenix]

(07-18-2023 12:17 AM)tangdfx Wrote:  Hi，Tony

Is it possibile that use only one PCB to replace the original two PCB design.

The bottom PCB only to provide the interface to printer and power source.

Unfortunately, no.

The CPU board emulates the PIK chip but does not provide a direct interface to the original printer circuitry, it has its own motor and print head drivers. It also uses a different type of power supply.

cheers

Tony

[teenix]

Getting a bit more done. The display seems to be behaving itself. The image shows up the serif's on the A(top) and D(bottom) segments.

Next is the keyboard and switch logic. This is a bit different to the other HP types of this era as they are multiplexed to share flag inputs on the ACT.

Somewhat cold in the van tonight - just under 6 degrees C - makes it hard to do much :-)

cheers

Tony

[Massimo Gnerucci]

(07-19-2023 01:23 PM)teenix Wrote:  Somewhat cold in the van tonight - just under 6 degrees C - makes it hard to do much :-)

I'd be glad to mix that with the temperatures we're experiencing now in Italy, so we could both relieve a little... ;)

[teenix]

Hi all,

The 19C instruction decoder, display and keyboard all seem to be working now. There were some issues trying to figure some things out but all good.

Next, I have to get the PGM/RUN switch working and then on to the complex issue of the printer.

I'm pretty sure the code that runs the printer in 97 CPU board replacement will do, with a few tweaks. I already have the 19C PIK printer ROM setup in the new processor. The hardware is much the same in both models so the 19C board has the same hardware drivers.

Some differences are that I don't have to reverse the printer motor, just change the return speed, there is a change in character count, and there isn't an out of paper switch, just a home switch.

cheers

Tony

[teenix]

A bit of one step forward, two steps back going on.

I placed my oscilloscope on the power in rail of my new HP-19C circuit.

I thought that when switching between Pgm and Run, the switch would maintain a solid power connection between these two positions. However, I can see a burst of noisy power spikes from ground to Vcc lasting around 20mS, and this will vary a bit depending on how fast the switch is moved.

The 60uF capacitor on the input of the original HP switching power supply probably deals with this, but on my circuit, it will cause a few headaches.

I sorted the problem, so lucky I saw this now, although a new PCB design is required.

While completing the menu software, I also noticed that one of the pins on the processor chip didn't support the function I assigned to it and I had to reassign it, so definitely need a new pcb design.

cheers

Tony

[teenix]

Hi all,

I installed the motor driver hardware onto the CPU board and connected the motor up.

The motor and printer HOME wire connections were a bit of a challenge because the original wiring is not soldered. It is used with small receptacles so that the wires can be removed and installed easily and allow separation of the two circuit boards. I managed to find some modern replacements though, so hopefully ok.

I cannot test the printer in its native environment because the original CPU board had failed. I was trying to repair this for someone, but the ACT had failed, and I found some bad RAM. This is what led to the 19C CPU replacement project which is now starting to come to life.

I plugged the motor in and powered up the CPU and printer boards. Activating new circuitry is always an eye wincing moment (for me anyway) and the hope is that smoke doesn't appear or things don't run erratically.

I was greeted by the "Error" display, so the CPU was working, (the Continuous Memory is ready but is switched off during testing), and the motor stayed off - good so far.

I wrote a small snippet of code so that I can test the motor from a command from the PC. I pushed the PC button and what do you know, it worked :-)

The motor control from the processor has 2 speeds, one for printing and one for homing the print head. Both speeds were working which is good because there is some board hardware, processor internal hardware and then the software controlling it, any one of which could have caused some fault finding.

From looking at a UTube video of the printer in operation, I cannot see a change in motor speed, but it is hard to determine. I do hear a sound change when the carriage is returning though.

Next is to test the print head home detect. This will be easier than the 97 printer I worked on, as you cannot damage the 19C printer mechanism if the motor does not stop at either end of its travel.

cheers

Tony

[tangdfx]

Great progress. Could I guess that I could get the new HP19C CPU board within six months？

[teenix]

(08-05-2023 04:57 AM)tangdfx Wrote:  Great progress. Could I guess that I could get the new HP19C CPU board within six months？

Hard to say. Once the printer is fully operational, it will only be a matter of testing.

I have all the printer code available from the HP-97 project, and it simulates ok, but in the real world there are probably differences required because of the smaller 19C paper size. I will have to try it out as soon as I can and adjust things accordingly.

I am also concerned about the printer if people operate the 19C on 4 x 1.5V batteries. The 19C was designed to run from 5V, not 6, so this may affect operation. I have a high current series diode in line with the battery which can be bypassed for 5V, or not for 6V.

cheers

Tony

[Chr Yoko]

Hi Teenix. About the 97 replacement MB.
Did you finally got some available microcontrollers ?
Or will you redesign the board around some more modern and available ships (stm32 or equivalent)?
I have a couple of fried 97 to revive ... ?

[teenix]

(08-05-2023 12:03 PM)Chr Yoko Wrote:  Hi Teenix. About the 97 replacement MB.
Did you finally got some available microcontrollers ?
Or will you redesign the board around some more modern and available ships (stm32 or equivalent)?
I have a couple of fried 97 to revive ... ?

Yes, I do now have parts available for the 97 CPU boards. The processor I use copes fine with the 97 operation. I have to admit I would find it hard work to change the processor and have to gear up and learn the intricacies and deal with the problems of a new one, better the devil you know :-)

cheers

Tony

[teenix]

Hi all,

Some more progress.

One of functions of the PIK chip is to sense the position of the print head and report back to the ACT if asked. It also checks the head position at power up and if it is not homed, it will try to make sure it gets back there ready for use. This is independent of the HP microcode. Actually, the HP microcode stays in an infinite loop if the print head does not home during printing.

My "PIK" just got this functionality enabled and it seems to be working fine. Unlike the HP code, I have time-outs which will turn off the printer of the head does not home, or it doesn't leave home when a print command is issued. The printer is then locked out of use until the calculator goes through a power cycle. If the problem exists, the calculator can still be used, but any time a print command is issued, the HP code won't get a command response back from the "PIK" and it will display "Error". The processor is internally set up to monitor the functioning of the printer while it is printing and if a fault is detected, the processor will do a full system restart and disable the printer from use until a power off/on cycle is executed. The fault condition is tested every few milli-seconds.

The next stage is nail biting. This is where the print heads get tested. Obviously, any failure here can destroy the head elements due to overheating from high currents passing through them for longer than the normal time. A high current power supply is also required.

First, I will test without them being connected and monitor the scope for proper signals coming from the head driver. These signals are pulse width modulated with the duty cycle dependent on the battery voltage. The duty cycle can also be changed slightly by the user to darken or lighten the printing, and the user can also adjust the print head speed while printing.

cheers

Tony

[teenix]

What a horrible place for a wire to break. It is pretty much inaccessible without breaking the HP-19C charger connector away from the casing. Attached image, yellow arrow.

Luckily, the terminal with the red arrow needed the repair. The tiny wires had frayed over the years, like what can happen on the 65 and 67, shown in the right side of the image.

I taped the charger wire to the casing to stop any further movement.

cheers

Tony

[teenix]

I managed to try out the printer without actually connecting the printer, just to see how the output is going to look like. I had to fool the HP microcode into believing that the print carriage was home when it asked, because there was no physical carriage just yet.

The image shows the calculator just being turned on with 0.00 on the display and pressing PRx.

The scope trace clearly shows the data that controls the head elements giving the required pixels for the print-out. The characters have the italic style and they look reversed because of the right to left movement of the print head. The right side of the image shows the pulse width modulation of the head signals, so that part of the hardware is functioning as well.

Next, I'll have to proceed with the actual printer, but I have to wait until the latest circuit boards arrive, hopefully by early next week.

cheers

Tony

[teenix]

Hi all,

While waiting for the new circuit boards (which should be here this afternoon), I have been playing with the 19C functionality.

By experimenting with the emulator, I have managed to add an extra 45 RAM registers and an extra 294 program steps. This system works similar to the HP-95C where you can have programs that operate in partitions. From the 19C's point of view, nothing has changed, it still works exactly the same as the original.

To accommodate this, I added 6 new key functions. These can be executed directly from the keyboard and can be added to a program and executed during program execution.

Because the 19C cannot accommodate these functions, because all keys are in use, I changed the way the [f] key works.

The 6 functions are:

Code:


  [f][f][0] CLRR  Clear secondary RAM or Program registers
  [f][f][1] RAND  Puts a random number in X, where 0 < X < 1
  [f][f][2] GTOP  GTO a program LBL Page 0 - 3
  [f][f][3] GSBP  GSB a program LBL Page 0 - 3
  [f][f][4] RPGE  Swap RAM or PGM pages - (similar to HP-67 P<>R key)
  [f][f][5] CONR  Place a stored constant into X, Constant Storage locations 0 - 9

Like the HP-95C you can run a program and GTO or GSB to more program data in a different partition.

A key entry example for GTO LBL5 in PGM Bank 2 would be:

Code:


  2
  5
  [f][f][2]

The PGM banks will be swapped, and the HP Microcode will search from Top of Program to find LBL 5, and the program would continue.
GSB works the same, and a RTN will jump back to the calling page.

If you want to swap RAM to Bank 2 in RUN Mode, press:

Code:


2
[f][f][4]

Only RAM memory $01 - $0F changes.
$00 can be used for the I pointer, so it stays as is

I might make an addition to [f][f][4] so that if you key in:

Code:


8 or 9
[f][f][4]

The RAM/PGM page can then be selected by the I register contents


If you want to write or edit a program in Bank 3, in RUN Mode press:

Code:


7
[f][f][4]

To recall constant[6] into X, press:

Code:


6
[f][f][5]

It all seems to work ok in practice, so I will recode it to run in the 19C CPU board.

cheers

Tony

[tangdfx]

Good. Tony.

It seems you can make a mini HP95C on HP19C platform.

[teenix]

Hi all,

I have populated the new boards.

I changed a few pin assignments on the processor so I will double check that the software matches then I will program it and try it out. I modified the display driver slightly as the LEDs were a tiny bit too dull. This display, like the Spice board, can be user set to Bright or Dim when in use.

As you might see, the interconnects between the display and print-head boards are using the original HP board connectors. There is no room for ribbon cables and no substitute for these that I can find. If the original boards are not functioning anymore, then these pins may as well be put to good use. It is not hard to solder them, you just have to make sure they are aligned properly which is easy to do.

If anyone wants a new board and doesn't trust their soldering, the pins can easily be de-soldered and mailed to me, and I will fit them.

Enough for today though :-)

cheers

Tony

[teenix]

Here's a couple of views of the new circuit boards fitted to the top case.

I can use this to verify the CPU operation, then I'll connect the printer and test that.

cheers

Tony

[teenix]

Yay :-)