Scratchpad and bintoascii in 20x2

[rolfi@tisco.no]

Hello,
I am measureing an analogue voltage, and displaying the value in a 4 digit 7-seg LED display. My H/SW is a 20x2 vs. c.0, and PE vs. 5.3.0.
A fairly straightforward task, but on my way, I have encountered a couple of 'strangeties' :
1. bintoascii on a wordvar using bptr (scratchpad, right?) does affect b0.
In essence, this is, what I did:
..
sertxd ("b0 before bintoascii: ",#b0,13,10)
bintoascii w5,@bptrinc, @bptrinc,@bptrinc, @bptrinc,@bptr
sertxd ("b0 after bintoascii: ",#b0,13,10)
..
I do not know if more regs are affected, just realized (after an hr's struggle..) that my flags got corrupted.. (Simulation , however, preserved b0..)

2. Unlike the chip, using the scratchpad mem with the simulator does not seem to work. I ran the following in the simulator and on the chip. No data could be found in the 'Memory'-window when simulating:
....
w5=12345
bintoascii w5,@bptrinc, @bptrinc,@bptrinc, @bptrinc,@bptr
bptr=3
@bptr="%"
bptr=0
sertxd (@bptrinc, @bptrinc,@bptrinc, @bptrinc,@bptr,13,10)
....

(The sertxd here is just for checking, and not used in the actual program, which is displaying w5 in a 4 digit 7-seg LED display)

Isn't there something odd here, or have I misunderstood the use of the scratchpad or anything else?

Where are the "variables" ptr, bptr, and timer3 located?
Thanks ..

 

[Technical]

You're not really understanding the use of the bptr and @bptr

bptr is a real variable. It can contain the number 0-127 on the 20X2.

@bptr is a virtual variable, which points to the memory address currently 'pointed to' by the value in bptr.

So if bptr is 0, @bptr will read or write the value at address 0. This is really the same as a peek or poke at address 0.

However as the lower addesses are also the variable b0, b1 etc, an @bptr write when bptr is 0 will also change b0, as address 0 and b0 are the same.

so
bptr = 0 : @bptr = 255
poke 0, 255
b0 = 255

are all exactly the same.


The same principles apply to the scratchpad, but then you use ptr and @ptr and get/put

 

[rolfi@tisco.no]

Thanks a lot! I did know the diff btw ptr and @ptr from my C-experience, but what I did NOT know, was the diff btw ptr and bptr. Knowing that bptr points to b0--> explains everything, I wrongly believed I was using the scratchpad!