Changes
The are two versions of Locomotive BASIC used in the Amstrad CPC and CPC+ computers. v1.0 is used by the CPC464, and v1.1 is used by the CPC664, CPC6128, CPC464+ and CPC6128+.
== BASIC v1.0 only ==
There is a region of memory between AC00-AC1B which is filled with RET instructions. The BASIC ROM calls the following locations:
AC01,AC04,AC07,AC0A,AC0D,AC10,AC13,AC16,AC19
It almost looks like these were used for debugging the ROM but were left in.
They can be used to implement new BASIC commands.
== Passing parameters to a RSX (Resident System Extension) command or binary function ==
with the help of that assembly code is it possible to find the parameters:
<pre>
ROUT1: CP "x" ;test register A if "x" parameters were hand-overedgiven, e.g. "x" = 2 RET NZ ; if no > failure and returnnot exactly x parameters then do not execute RSX.
LD L,(IX+0)
LD H,(IX+1) ; HL = value of last parameter
A register holds the number of parameters. IX points to each parameter. IX+0/IX+1 is the last parameter. This happens because each parameter in order is pushed onto the stack and IX then points to the last parameter pushed. Each parameter is a 16-bit value.
If a parameter is a string, then IX holds the 16-bit value is an address of a "the string descriptor which point to a 3 byte block". The first byte of the string descriptor is the length. The next 2 bytes are an address that point to the string in memory.
With the help of the variable container "@" it is also possible to get a result from an invoked mc-code back to basic.
In this case the param parameter contains the address of the integer, floating point or string. You can modify these to give the result.
BASIC allocates the strings, so when you modify a string, do not write more characters than the original string.
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== Entering BASIC programs ==
A maximum of 255 characters can be entered for a single BASIC line.
| INPUT
|-
| &a4
| KEY
|-
|-
| &b5
| ON SQ
|-
| &b6
|}
*This token identifies a integer (16-bit) number. The two bytes following this token is the number, stored low byte then high byte. e.g. &191a,&2d,&00 represents the integer number "&002d"="45".
*This token (&0B) is changed at run-time to &0D
*This token identifies a integer variable. 02,00,00,var name offset to number in program setup when program RUN. The variable name is stored directly, with bit 7 of the last character set.
