88-UIO: two boards in one

Altair 8K BASIC 3.2 loads from a cassette through one 88-UIO board.

cd examples/uio
altairsim uio.toml

The machine stops at the BASIC prompts. Press Enter at MEMORY SIZE? and at TERMINAL WIDTH?. Type Y at WANT SIN-COS-TAN-ATN?. BASIC then prints:

10312 BYTES FREE

ALTAIR BASIC VERSION 3.2
[EIGHT-K VERSION]

OK

What is different

The built-in basic8k machine needs two boards. An 88-2SIO is the console. An 88-ACR is the cassette. This machine has one board, the MITS 88-UIO, which does both jobs.

• The 6850 serial port of the 88-UIO responds to port 0x10. This is where Port A of an 88-2SIO responds. The serial port is the console.
• The cassette section responds to port 0x06. This is where an 88-ACR responds. The cassette section is the tape.

Both sections use the standard ports. Therefore the MITS bootstrap LDR8K32.HEX runs without a change. 8K BASIC does not know that one board does both jobs. The sense switches are 0x8C. The header of the loader gives this value: A15 selects load from cassette, and A11 and A10 select an 88-2SIO terminal.

Try it

Type a program at the OK prompt:

10 PRINT 6*7
20 PRINT "TAPE OK"
RUN

An 88-UIO can do things that an 88-ACR cannot. Press Ctrl-E to get the monitor, then type:

SHOW uio0                 ; show both sections: serial_port, port, standard, motor
SET uio0 standard=kansas  ; use the Kansas City standard (2400/1200) for the modem
REWIND uio0:tape          ; put the tape back at the start

Ctrl-E returns you to the altairsim> monitor at any time.

Files

The processor runs at full speed, and the tape loads in about one second. To run at the 2 MHz speed of the real machine, type SET cpu0 clock_hz=2000000. A 300-baud cassette then takes about 90 seconds to load.