The Amstrad PCW 40028 (or Gate Array) is a custom-designed chip (ASIC) fundamental to the architecture of the PCW8256, 8512, and 9512 computer family. This component integrated multiple functions into a single package to drastically reduce manufacturing costs and motherboard complexity.
Below is the technical information and available references:
Main Functions of the Gate Array (40028)
This chip acts as the logical "heart" of the system, managing the following critical areas:
- Video Controller: Generates the signal for the high-resolution monochrome monitor (720x256 pixels) and manages the Roller RAM, a 512-byte memory section that allows fast screen scrolling.
- Memory Management (Bank Switching): Allows the Z80 processor (8-bit) to access more than 64 KB of RAM through memory bank switching, supporting up to 512 KB in models like the 8512.
- Floppy Drive and Printer Controller: Integrates the logic to handle 3-inch drives (or 3.5" in later models) and communication with Amstrad-specific dot matrix or daisy-wheel printers.
- Interrupt Logic: Manages the timing and signals necessary for coordinated hardware operation.
Manufacturing Details
- Design: Commissioned by Amstrad to MEJ Electronics, the same firm that developed the Amstrad CPC 464 hardware.
- Variants: Although the 40028 is the most common in the 8000/9000 series, minor variants exist depending on the motherboard revision (such as the 40010 used in CPC models, which shares similar design principles).
- Packaging: Generally presented as an SMD chip (surface mount) in later revisions or as a large DIP chip on early boards.
The Gate Array is the integrated circuit responsible for most of the PCW's functions.
To further explore the programming of this chip, it is recommended to consult the Amstrad PCW Hardware Reference, which explains how to manipulate the Gate Array registers through I/O ports (such as port &F5 for the Roller RAM).