- 20 -
C. Loading and Using 8K BASIC from Cassette
In this demonstration, we will load 8K BASIC Version 4.0 from a cassette tape
file. The 88-ACR cassette interface for the Altair consisted of an audio
modulator/demodulator board that connected to a standard cassette recorder
and to an 88-SIO serial interface board. The SIO board provided the data in-
terface with the Altair bus. The digital content present on the cassette tape
for loading BASIC was the same data and format as used on paper tape.
In this exercise, we will not use the cassette player and tape itself, but
instead send the data contained on the cassette through the same SIO board
and port addresses as used by the 88-ACR cassette interface (the Altair won’t
know the difference!) A separate serial port is used to connect to the opera-
tor’s terminal.
Note: If you have the optional Audio Cassette Interface for the Altair Clone,
this same demonstration is present in the Cassette Interface User’s Manual
using a real cassette and tape player!
Computer Configuration
Serial port 1 on the Altair Clone (the upper DB-25 connector) should be
configured as a 2SIO serial port at octal I/O address 20/21. This port
serves as the operator’s terminal. This is a standard Altair configura-
tion. This is also the default Altair Clone configuration for port 1.
The cassette data comes in on serial port 2 (the lower DB-25 connector)
which should be configured as an SIO board at octal I/O address 6/7. This
is the standard cassette configuration in the Altair. This is also the de-
fault Altair Clone configuration for port 2.
You can confirm or change the Clone’s serial port configuration if needed.
See “Serial Port Menu” in Part 2, “Configuration Monitor” of this manual.
The default baud rate for the cassette SIO port on the Clone is 9600 baud.
While this is much faster than the 300 baud at which the real cassette in-
terface operated, we recommend using 9600 baud for this demonstration.
Buffering in the PC’s serial port drivers and issues with some USB-to-
Serial adapters can make operation at 300 baud problematic.
Terminal Emulator Configuration
The TeraTerm terminal emulator is used to duplicate the functionality of
both the operator’s console and the cassette player. First, start an in-
stance of TeraTerm to use as the operator’s console. Then, start a second
instance of TeraTerm to use as the cassette player. You’ll probably re-
ceive a “Cannot Open Serial Port” error when you open the second TeraTerm
window. In the second window, go to the “Setup->Serial Port” menu and
choose the COM port that serial port 2 from the Clone (the cassette inter-
face) is connected to.
In the console TeraTerm window, choose “Setup->Serial Port” and set the
“Data” field to 7 bits, the “Parity” field to “Space” and verify the baud
rate is 9600. Also confirm that the “Transmit Delay” fields are both set
to zero.
In the cassette TeraTerm window, confirm serial settings of 9600 baud, 8
bits, no parity and one stop bit. Also confirm that the “Transmit Delay”
fields are both set to zero.
To load 8K BASIC, we must first enter a small program via the front panel
called a “bootstrap loader.” The job of the bootstrap loader is to receive a
second loader from the tape called the “checksum loader.” The checksum loader
is at the beginning of the BASIC tape. Once the checksum loader has been read
To Next Page
