TRS-80 Model I info (RE: MSX, TRS-80, Colour Genie, etc.)

The Model I originally shipped without a numeric keypad. To the right of the main keyboard was a rectangular keypad-size plaque reading "Radio Shack TRS-80 Micro Computer System". The numeric keypad was added to later models, and was available as a retrofit kit for around $50. With the numeric keypad installed, the nameplate was moved to a horizontal plaque above the keyboard. The TRS-80 Model I lineage includes: Model I, 4K, Level I BASIC - This is a 3-piece system with the computer in the keyboard. It includes the system keyboard/cpu, monitor, tape drive (actually a rebadged regular Radio Shack portable cassette deck with no modifications), and power supply brick. Level I BASIC is similar to Tiny BASIC. I still have my Level I BASIC reference manual. Model I, 16K, Level II BASIC - The 16K and Level II upgrades went together. 16K is the maximum Model I memory in the system unit (8x 4116 DRAMs). Level II BASIC is similar to Microsoft BASIC/80 with functions added for things like the TRS-80's 128x48 memory-mapped monochrome graphics. Level II also added a keyboard debounce routine--Level I machines were very difficult for typists. Other Upgrades: - Expansion Interface Matching silver color, acts as a monitor stand, connects to system unit via ribbon cable. Contains dual floppy controller (WD chip), sockets for an additional 32K (2 banks of 4116 DRAMs) for a system maximum of 48K, and a parallel connection. 16K ROM BASIC occupied the remainder of the address space. The expansion interface also contains a card bay for an RS-232 interface. - RS-232 interface board For expansion interface. - Floppy drives Single-sided single-density, approx. 90KB free space. - Lower case upgrade Provides lower case capability. - Numeric keypad retrofit As discussed above Known TRS-80 Model I problems: - Unreliable cassette interface. Radio Shack later released a modification that improved this somewhat. The best option is a third-party unit called the Data Dubber by Microperipheral Corporation (I worked there!) that went in between the system unit and cassette and squared the wave. - Wonky, unbuffered connection to Expansion Interface. This went through various modifications, and some cables you'll see have big buffer boxes in the middle. Later Expansion Interfaces had built-in buffering. Some bought third-party expansion interface clones from Lobo and others. Be very careful if you get an Expansion Interface without a cable. It might need the buffered cable, and it would be a pain to manufacture. - Bad data separator chip. The stock data separator was unreliable. Most people replaced theirs with a third-party improvement such as Percom's. - Unreliable connection for the Expansion Interface-mounted RS-232 board. This board slipped over vertical post connections and never made good contact. Most folks used third-party alternatives that worked off the cassette port. Kai