I don't think the full extended basic is an option since I am trying
to squeeze a program into 4K (it might be too large for that already).
There is one extended basic on the German VZ site if I remember
right. Not sure if it's the same one you are talking about.

If VARPTR still executes when it's pre-tokenized outside the VZ then I
could just do that. USR is listed in the VZ300 manual. Is that a
mistake?

No need to look up the CLS # code. Using existing code is fine... if
it's available. The code I posted is CLS # without figuring out the
character. I had that in the basic subroutine.

The assembly I posted has a tiny issue... or should I call it a big
issue. SCRNSIZE 512... Yeah... like that will work on an 8 bit.
I also didn't preserve registers but I'm not sure if I need to.
The fixes are below for a full CLS # USR call. Now the string to hold
it will need to be longer than the max line length for the VZ editor.
Around 37 bytes +-. Just remember that I haven't programmed a Z80 in
years... this could be wrong. Oh, and no validation of the parameter
takes place.


USRPARM equ 31009 ;location USR parameters are passed
SCREEN equ 28672 ;screen address

start:
PUSH AF ;store registers, this should have been 1 instruction
PUSH BC
PUSH HL
LD HL,chartable ;point to the character table
LD BC,USRPARM ;load the USR call parameter.
ADC HL,BC
LD A,(HL)
LD B,0 ;loop counter. we want 255 loops x 2 for screen size
LD HL,SCREEN ;point to the screen
loop1: ;clear 1st half of screen with this loop
LD (HL),A ;store the character in screen memory
INC HL ;point to the next screen address
DJNC loop1 ;decriment b and loop if it's not 0
loop2: ;clear 2nd half of screen with this loop
LD (HL),A ;store the character in screen memory
INC HL ;point to the next screen address
DJNC loop2 ;decriment b and loop if it's not 0
POP HL ;restore registers
POP BC
POP AF
RET
chartable: ;contains character codes for CLS # 0-8
DEFB 96,143,159,175,191,207,223,239,255


--- In vzemu@yahoogroups.com, "Leslie Milburn"
<lwm317_ebayaccount@...> wrote:
>
> Hi James,
>
> Firstly I would suggest that you install Steve Olney's Extended
BASIC as it
> gives you most of the missing TRS80 commands including VARPTR and will
> probably make your life a lot eaiser. Hopefully someone has that
available
> somewhere as I will not get around to the software uploads for quite
a while
> yet.
>
> Secondly Larry Taylor wrote an article in one of the magazines (was it
> Australian Electronics Monthly ??) to provide a CLSn command.
> I will try and see if I can find it and scan it in.
>
> Leslie.
>
> ----- Original Message -----
> From: "James Diffendaffer" <jdiffendaffer@...>
> To: <vzemu@yahoogroups.com>
> Sent: Tuesday, August 05, 2008 2:41 PM
> Subject: [vzemu] VARPTR & USR(X)
>
>
> > Ok... the manual isn't the greatest so let me see if I have this right
> >
> > The program I'm porting uses the TRS-80 CoCo/MC-10 command CLS# to
> > clear the screen to a particular color. The VZ spit that back and I
> > wrote a basic subroutine to duplicate it but I want to use VARPTR to
> > place a USR function in a string so it's fast.
> >
> > VARPTR returns the location of the string structure whitch is the
> > string length followed by the actual location of the data held by the
> > string. At least if it duplicates the Model 1.
> >
> > structaddress = VARPTR(MyString$)
> > stringaddress = (structaddress+1)+((structaddress+2) * 256)
> >
> > Then poke the bytes of the machine code into the string.
> >
> > POKE the string address into 30862-30863 since in now contains our USR
> > function.
> >
> > 31009-10 holds the parameter X value on a USR(X) call.
> >
> > So... the assembly code I need should be something like this:
> >
> > ;I'll deal with syntax when I get there
> > USRPARM equ 31009 ;location USR parameters are passed
> > SCRNSIZE equ 512 ;32 characters * 16 rows = screen size
> > SCREEN equ 28672 ;screen address
> >
> > start:
> > LD A,USRPARM ;load the USR call parameter low byte, high is unused.
> > LD B,SCRNSIZE ;screen size in bytes for counter
> > LD HL,SCREEN
> > loop:
> > LD (HL),A ;store the character in screen memory
> > INC HL
> > DJNC loop
> > RET
> >
> > Does that look reasonable? Should be pretty small byte wise. I'm
> > guessing under 20 bytes.
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>