Exidy Sorcerer - Description

Description

The Sorcerer was a combination of parts from a standard S-100 bus machine, combined with their custom display circuitry. The machine included the Zilog Z80 and various bus features needed to run the CP/M operating system, but placed them inside a "closed" box with a built-in keyboard similar to machines like the Commodore PET, the Commodore 64, and the Atari 8-bit family. Unlike those machines, the Sorcerer's keyboard was a high quality unit with full "throw". The keyboard included a custom "Graphics" key, which allowed easy entry of the extended character set, without having to overload the Control key, the more common solution on other machines. Somewhat ahead of its peers, the Sorcerer included lower case characters as a standard feature.

Unlike most S-100 CP/M machines of its era, the Sorcerer did not have any internal expansion slots, and everything that was needed for basic computing was built-in. A standard video monitor was required for display, and optionally a standard audio cassette deck was needed for data storage. The Sorcerer included a small ROM containing a simple monitor program which allowed the machine to be controlled at the machine language level, as well as load programs from cassette tape or cartridges. The cartridges, known as "ROM PAC"s in Exidy-speak, were built by replacing the internal tape in an eight-track tape case with a circuit board and edge connector to interface with the Sorcerer.

The machine was usable without any expansion, but if the user wished to use S-100 cards they could do so with an external expansion chassis. This was connected to the back of the machine through a 50-pin connector. Using the expansion chassis the user could directly support floppy disks, and boot from them into CP/M (without which the disks were not operable). Another expansion option was a large external cage which included a full set of S-100 slots, allowing the Sorcerer to be used like a "full" S-100 machine. Still another option combined the floppies, expansion chassis and a small monitor into a single large-ish box.

Graphics on the Sorcerer sound impressive, with a resolution of 512×240, when most machines of the era supported a maximum of 320×200. These lower resolutions were a side effect of the inability of the video hardware to read the screen data from RAM fast enough; given the slow speed of the machines they would end up spending all of their time driving the display. The key to building a usable system was to reduce the total amount of data, either by reducing the resolution, or by reducing the number of colors.

The Sorcerer instead chose another method entirely, which was to use definable character graphics. There were 256 characters possible for each screen location. The lower half was fixed in ROM, and contained the usual ASCII character set. The upper half was defined in RAM. This area would be loaded with a default set of graphics at reset, but could be re-defined and used in lieu of pixel-addressable graphics. In fact the machine was actually drawing a 64×30 display (8×8 characters) which was well within the capabilities of the hardware. However this meant that all graphics had to lie within a checkerboard pattern on the screen, and the system was generally less flexible than machines with "real" graphics. In addition, the high resolution was well beyond the capability of the average color TV, a problem they solved by not supporting color. In this respect the Sorcerer was similar to the PET and TRS-80 in that it had only "graphics characters" to draw with, but at least on the Sorcerer one could define a custom set. It was also possible to provide animation by character replacement or by redefining the character bitmap.

Given these limitations, the quality of the graphics on the Sorcerer was otherwise excellent. Clever use of several characters for each graphic allowed programmers to create smooth motion on the screen, regardless of the character-cell boundaries. A more surprising limitation, given the machine's genesis, is the lack of sound output. Enterprising developers then standardized on attaching a speaker to two pins of the parallel port, which users were expected to supply.

A Standard BASIC cartridge was included with the machine. This cartridge was essentially the common Microsoft BASIC already widely used in the CP/M world. One modification was the addition of single-stroke replacements for common BASIC commands, pressing GRAPHICS-P would insert the word PRINT for instance, allowing for higher-speed entry. The machine included sound in/out ports on the back that could be attached to a cassette tape recorder, so BASIC could load and save programs to tape without needing a disk drive. An Extended BASIC cartridge requiring 16 KB was also advertised, but it is unclear if this was actually available; Extended BASIC from Microsoft was available on cassette. Another popular cartridge was the Word Processor PAC which contained a version of the early word processor program Spellbinder. A constant ROM fault in the wordprocessor PAC was a printer status switch setting for the printer, but most people learned about it and turned it off early in their power-on.

The Montfort Brothers made an EPROM PAC with a rechargeable battery inside and 16 kB RAM with an external write-protect switch. Thus bootable software could be uploaded to the pack and kept for a longer period.

Many CP/M machines were designed to allow the full 16-bit address space of 64 kB to be populated by memory. This was problematic on the Exidy Sorcerer. 32 kB could easily be populated. Another 16 kB was the ROM cartridge address space. This could be populated, but required disabling the ROM cartridge capability. The last 16 kB was required by the system for I/O, particularly for the video, and would have required extensive system modification.