After the successful PC-121x series, the PC-1500 was the second pocket computer released by Sharp, and their first one based on an 8 bit microprocessor. It might be contended that the PC-1500 was THE milestone in pocket computers. It was very popular among computer hobbyists, and it was used by many companies who equipped their field staff with the machine.
Why was this so? Actually, the technical specifications were not overwhelming: its display was only two characters longer than its predecessor's, but at least it featured "one line graphics", i.e. it was a "gap-less" display with 7 x 156 pixels.
With 3.5 KB memory, the PC-1500 had not much more RAM available for BASIC (1850 bytes) than the PC-1211 (1424 steps). Moreover, it was quite bulky (25 mm thick, 375 g), supposedly mainly because it used 4 normal AA batteries as power supply. However, the latter fact might have been an advantage, as these batteries are cheap and easily replacable.
Presumably, the most important advantage was the expandability of the system. Several RAM extensions (some even with battery back-up), program modules, a "docking station" with cassette interface and colour plotter with full graphics capabilites accessible with BASIC, an external board with programmable function buttons, various interfaces etc. were available. Moreover, the PC-1500 was also programmable in machine code. Apart from that, nothing comparable was available from other manufacturers at that time. Later strongest competitor Casio had their FX-702P, and they were only about to release their PB-100 which had rather weak specifications.
The PC-1500 was released in late 1981 in Japan and early 1982 in the rest of the world. It was built around the LH 5801 8-bit CMOS processor which ran at 1.3 MHz. The RAM consisted of three parts. The 1KB system RAM was made up by two TC5514 1k x 4bit chips, a legacy from the PC-121x series. This area was used for system memory and part of the fixed variables. User RAM was realised with a HM6116 2k x 8 bit chip, most of it available for BASIC (1850 Bytes). Additional 512 Bytes incorporated in the display driver chips were used for the rest of the fixed variables and the display buffer.
The RAM could be expanded by RAM modules in different sizes, the largest of which was 16KB (actually, there was also a 32KB module, which had two switchable 16KB pages, i.e. only 16KB could be used at a time). There was also a widely known method to build a self-made RAM expansion up to 32KB.
As with the PC-1211, there was a custom manufactured version of the PC-1500 built by Sharp for Tandy Radio Shack, called the TRS-80 PC-2. Apart from a different keyboard layout, it was identical.
Two years later, the slightly expanded model PC-1500A was released (in Japan and maybe some other countries labelled as PC-1501). It was equipped with four HM6116 RAM chips, which made 5946 Bytes available for BASIC, and an additional 1KB area for machine code only.
Thanks to Roman von Wartburg and his site for information and picture.