trs-80

KiCad Design Files for the LH5801 Sharp Microprocessor

/ Kai / 2 Comments

I’m currently working on a custom development board, based on a quarter of a century old microprocessor, the Sharp LH5801. This microprocessor is the heart of the Sharp PC-1500(A) Pocket Computer, also known as Tandy TRS-80 Model II.

I’ve got plenty of documentation on the processor and the Sharp PC-1500, but what I did not have was a spare processor to play with. Recently, I got hold of a dozen of them, so no excuse anymore for not playing with them. 🙂

I started the design process by measuring out the package size in mm and wondered about the strange results I got… Well the size of LH5801 package is – bang on – 0.7 inches. It also has an odd number of pins for such a package size: 76 pins. Both make it pretty impossible to use the standard footprints provided by various package libraries. At least a short round of googling for packages for Eagle CAD or KiCad was unsuccessful.

So I had to design my own footprint which was smoother than expected. I used a already present layout with the correct footprint pitch and adapted copied/adapted the pins.

The part was made with KiPart (based on a CVS table).  The pin description and layout was taken from the Sharp PC-1500 Technical Reference Manual.

The resulting KiCad part and footprint is in my Sharp PC KiCad Library at GitHub.

Sharp PC-1500/1600 ROM Dump Method 2: Desoldering the ROM Chips

/ Kai / 4 Comments

To make it clear from the beginning: this is a (possibly) destructive method of reading ROM chips. The process of extracting and possibly a resoldering of the memory chip might fail. In my case I’ve tested it on two Sharp CE-150 PCBs I’ve declared to be spare parts. It is only a proof of concept as there are simpler non-destructive ways of ROM extraction on a Sharp PC. I was just curious and so I’m describing my experiences.

Well… At first I did not want to desolder the ROMs: I started with the intention to use a set of probes attached to the individual pins of the chip to read the content of the Sharp PC / CE ROM chips. This did not work due to the narrow leg distance of the QFP chips (0.8 mm).

Probe Connection Problem

Desoldering QFP chips can be done rather quickly with a hot air gun. At least that’s the most comfortable way I know of. I usually add some flux and in some cases larger quantities of leaded solder. The latter decreases the melting point and speeds up the process. I don’t care about solder joints as the chips and the pads can easily be cleaned after the removal. Excessive amounts of solder can be removed with flux and a clean soldering iron tip.
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Sharp PC Audio Output (CMT-OUT) Simulation in LTspice

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This was a little test out of curiosity… I’m currently playing around with an amplifier circuit for the Sharp CE-150 audio output (CMT-OUT) and wanted to see if the signal I’m getting is already distorted when leaving my Sharp PC, or if my circuit and/or sound card is causing the distortions.

The CE-150 uses Frequency Shift Keying (FSK) to transfer binary data via audio signal (e.g. to a tape recorder). It sends four pulses of 1.27 kHz for a binary “0” and eight pulses of 2.54 kHz for a “1”.

Sharp CMT-OUT LTspice Schematic

To test the circuit I’ve taken the original design and simulated the circuit in LTspice (running under Linux with Wine). This tool allows the simulation of various analog (and digital) circuits – perfect for my test.

Sharp CMT-OUT LTspice Plot

Sharp CMT-OUT Audacity Plot

The result was – to be honest – pretty surprising for me. The upper screenshot shows the LTspice simulation of the output signal, the lower screenshot was taken from a WAV file in Audacity. I was not only able to simulate the circuit but also to use the resulting signals as a good approximation for my amplifier circuit (not shown). 🙂 One minor fix (also not shown) left was to adapt the transition time between a “0” and a “1” to better fit to the original curve.

Sharp PC-1500/1600 ROM Dump Method 1: Audio Transfer via CE-150 Extension

/ Kai / 6 Comments

In this post I’m describing a method which is widely used to Dump RAM and ROM images on Sharp PC-1500 and PC-1600 systems. This method is non-destructive and can be used on most Sharp PC ROMs and extension cards. It only requires a Sharp CE-150 extension, an audio cable, and a computer with a microphone input (i.e. sound card).

Besides a plotter, the CE-150 Color Graphic Printer also provides two audio interfaces (line-in and microphone output). These were (and still are) used to transfer code or data between Sharp PCs and tape recorders. Today, such recorders are mostly outdated but the method works nonetheless with sound cards. Software tools are freely available (e.g. pocket-tools) that allow the transformation of recorded audio files into binary dumps and even further into BASIC code.

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Sharp PC 1500/1600 Schematics Collection

/ Kai / 3 Comments

To facilitate the access to Sharp Pocket Computer schematics I’ve started to collect and mirror some of them on my web site. This should allow Sharp PC 1500/1600 enthusiasts to update, modify, and especially to repair their hardware.

The Sharp PC 1500/1600 series are obsolete hardware. Their schematics are already freely available on the internet and therefore considered to be in the public domain. Please inform me if you own a copyright on some of this material and do not want it to be available on my web site.

HIF6A-60PA-1.27DS as Replacement for JAE PICL-60P-LT Sharp-PC Connector

/ Kai / 1 Comment

Needing a replacement for the long ago discontinued Sharp-PC connector JAE PICL-60P-LT, I dug through a lot of datasheets and finally found a pin-compatible one:

Hirose HIF6A-60PA-1.27DS – Datasheet
Hirose HIF6A-60PA-1.27DS – Digi-Key Link

The connector fits good enough for my purposes. If necessary removing a bit of the plastic case left and right of the pins improves the connectivity as the replacement connector is a bit broader.

There is also a version with mounting holes (HIF6B-60PA-1.27DSL) which I will also try to get my hands on (currently not in stock).

My original solution was to use a 2×30 1.27×2.54 pin header as shown in this post, but the narrow space between the pins led to serious constraints in designing a new interface board (more about that when it’s ready).
HIF6A-60PA-1.27DS JAE PICL-60P-LT 1