Sharp PC-1404G / 1405G - The AA experiment

Top: Sharp PC-1404G

Bottom: Sharp PV-1405G. Yeah, it's in rough shape

Hello, Friends!

In Japan back in 1984/85, Sharp released two models in their PC-1400 line, the PC-1404G and PC-1405G. A cursory glance at one of the units from the top would suggest a budget model similar to the PC-1430, and the comparison has merit. Both units have reduced functionality and memory compared to the family progenitor, the PC-1401. The view from the side reveals something strange; the units are quite a bit bigger than your standard 1401. 

Put on a bit of weight there, mate?

Size comparison PC-1404G to PC-1401

That size increase comes from the battery compartment, a case extension which is designed to take 2 AA batteries. Indeed, that is the only actual difference between these units and the rest of the line physically. As for the why, two reasons jump to mind: battery life and the long term costs of replacing those batteries. These units were 'G' units, designed with Japanese schools in mind. Probably for maths and getting acquainted with programming fundamentals. 

If you grew up back in the era, you probably remember just how expensive batteries used to be, especially coin cells like the CR2032. Then there is the issue of supply. I have no idea how it was in Shōwa era Japan, but least in 80s Germany, you weren't going to get coin cells at your local discounter, and the price was around €10-12 per battery! (source Quelle catalog 1986). AA batteries were much easier to source.
With the 1404/05G, Sharp effectively upped battery life, while also reducing the cost and effort to replace them. This meant sacrificing portability, but for a school, it might not have been that big of a problem to use them as desktop units. The form factor certainly makes for easier reading of the LCD. 

Looking at the hardware side of things, the 1404G is powered by Sharp's (or rather Hitachi's) Wunderkind CPU, an 8 bit SC61860 running at 768 kHz, a speed bump from the 576kHz of the PC-1401. RAM is a paltry 2kB, of which 1486 bytes are usable. There is an unpopulated spot on the mainboard which could probably take a further RAM chip, but I haven't tried it, so I can't vouch for feasibility.  ROM on both units is 24kB. Neither unit comes with a piezo buzzer, probably to preserve the sanity of teachers, but BEEP is implemented in BASIC and if you want, you can attach a piezo buzzer to pin 3 and 7 of the 11-pin I/O port internally. There's certainly enough room for one. 

The inside of my PC-1404G. The SC61860 CPU can be seen to the left of the piezo buzzer

The LCD on both units is a 16 character, 5x7 dot matrix affair. It was not designed for these models and is certainly repurposed from a different model. I say this because there are indicators on the LCD which aren't used. The HEX, parenthesis, M and Calc mode indicators are superfluous here, neither unit has a Calc mode. The same LCD was also used in the PC-1430/31. It is pin compatible with the 1401 LCD, and that is the one my PC-1404G now has.

It's a bit of a mystery where the LCD originally belonged, because I have every 14xx model Sharp produced, and it isn't a fit for any of them. If you happen to know where it originated, please comment below. 

A UV close-up of the LCD, bottom left the unused CALC indicator; up in the middle the unused HEX mode.

If we take a closer look at the 1405G, we see that Sharp has opted for a 4-bit SC61720 with a 1MHz clock speed. Sharp's 4 bit models are much snappier than their 8 bit brethren. A 1000 iteration FOR-NEXT loop on the 1405G takes 4.5 seconds, compared to 6.5 seconds on the 1404. The speed boost is mostly due to the 1 MHz clock and to a lesser degree, the faster BASIC implementation. 

You only get 1254 bytes of usable memory on the 1405G, as with the 1404G, there is an unpopulated space on the board that probably could fit a further RAM chip, along with a few bridges that might be configured to use it, but with no information for such a mod at hand, this is complete assumption on my part. 

The Sharp PC-1405. The heart of the unit is a 4-bit SC61720 CPU running at 1MHz. Quite empty in here.

The rather small size of the ROM compared to the 1401 should make it clear that you wont be getting the full BASIC experience. Many functions are missing. No ASC, CHR$, LEFT$, RIGHT$ or STR$. Although you can use "&" to convert from hex to decimal, there is no functionality to do the reverse.

At least with the PC-1404G, you get usable PEEK, POKE and CALL functionality; the 1405G isn't so amenable. 

These are quite the interesting Pocket Computers, but I wouldn't go out of my way to get one unless you're a hardcore collector. Your chances of finding one outside of Japan is pretty much zero, and even in Japan, I have seen these units pop up exactly once on Mercari. 

Still, the idea of converting a Pocket to run on AA cells is quite intriguing, and if I still worked in a lab, I think a converted 1403H would be an awesome little unit to have.