Changes

Both methods can represent the same data, so there is no advantage to using either. The original reason for the two methods is due to the original method to playback the sound. Modern sound cards can play both methods of data storage.

When the writing of a program is completed a "master" cassette is created. This cassette contains a audio representation of the computer data.

If you are transfering a cassette using samp2cdt, then you are advised to use an original (i.e. a cassette created directly from a master cassette), or a first generation copy (i.e. a cassette copied from an original).

A "loader" is the name given to a program that reads data from cassette into the computer memory.

You can test if the computer is operating in cassette mode by typing RUN". If you see "Press PLAY then any key", then the computer is operating in cassette mode. If there is an error, then the computer is not operating in cassette mode.

The audio from the cassette is read from a cassette player through the Amstrad's cassette electronics.

The resulting measurements can be read using the following Z80 instructions:

ld b,&f5 ;; I/O port address for PPI 8255 port B

;; (PPI 8255 port B is operating as input.)

in a,(c) ;; read port B inputs

and %10000000 ;; isolate bit 7 which contains the measurement.

This measurement is *not* the actual state of a data-bit, but represents a low ("0") or high amplitude ("1"). In this document, the value of this measurement will be refered to as a "high" ("1") or "low" ("0") level.

* if the amplitude is -128..0 then the final measurement will be "0".

A waveform is written to cassette using bit 5 of port C of the 8255 PPI IC. The waveform can only be defined by a high or low level, defined by the state of bit 5, which is then converted by the Amstrad's cassette electronics into a final output amplitude which is recorded onto cassette.