Processor The Compukit UK101 is powered by a
6502 microprocessor CPU running at 1
MHz, and is equipped with up to 8
kilobytes of
RAM using 2114
static RAM chips of 1024×4-bit. An additional memory-mapped 1 KB of RAM is used for the video display. It has the
8K Microsoft BASIC interpreter stored in
ROM. In addition to Basic, a 6502
machine code monitor (2K bytes) is built into ROM. It allows programming by entering sequences of 6502
opcodes. Later a
two-pass assembler was available which allows the use of
assembly language. Although the 6502 has two
interrupt input pins (
NMI and
IRQ), neither is used by the UK101.
Display The UK101 has a 16-row, 48-column
memory-mapped character semigraphics display, with each character taking up 8x8 pixels with an
aspect ratio of about 1:2 (corresponding to an effective resolution of 384x128). CPU access to video memory causes noticeable glitches (known as "snow") on the screen.
Keyboard The keyboard of the UK101 is located on the main
PCB, and comprises a matrix of keyswitches. The matrix is interfaced to the CPU via two 8-bit I/O ports, and is
polled by firmware in the machine's ROMs. One key is a latching type, the shift-lock key. When supplied as a kit, the keyboard was assembled by the purchaser from a bag of switches and keytops. The keyboard ports are located at address DF00 (
hex), or 57088 (decimal).
BASIC programs typically poll for real-time keyboard input by using the
PEEK and POKE commands at that address. Because the keyboard lacks any way to generate an interrupt, it is not possible to implement a
typeahead buffer. The keyboard matrix also lacks any
diodes at the intersections of the matrix. This leads to problems when reading certain combinations of keys pressed simultaneously. The matrix was designed to allow only the shift, control and shift-lock keys to be pressed simultaneously with another key. The keyswitches themselves were originally manufactured by Cherry.
Program Storage In common with other home computers of the time, software can be saved and loaded on standard cassette tapes. The UK101 uses the
Kansas City standard tape format. I/O is managed by a
Motorola 6850 ACIA. This allows a full
RS-232 port to be implemented, with the addition of a few extra components and minor modifications to existing jumpers on the board.
Compared to the Superboard Although very similar to the Ohio Scientific Superboard II, the Compukit UK101 differed from that machine in a few places: • Video display of the UK101 works at UK frequency and resolution. • RF output is
UHF (channel 36) to suit domestic TVs in the UK. • Power supply is located on the main PCB and accepts UK 240v AC mains input, via an external 9v AC transformer. • Display improved to 16 lines of 48 characters per line. • Memory increased to 8 KB. However, similarities in the PCB layout make it clear that this machine is a clone. The people involved with the modifications were
Chris Cary and Bill Wood. == Expansion ==