HP97 The journey begins

[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