Address
is the address of the Video Memory and send is the byte sent
out port 0.
address = $100 * ( send + $c0 ) send = address - $c000 $100
Port 1 - Key Port
Port 1 is used for the keypresses. If you don't remember us
talking about that, look back at the keypress
section. I went into some pretty good detail about it.
Port 2 - Contrast
Port 2 is used to adjust the contrast. It is another write-only
port. You can send any value between 0 and 31 to specify different contrast
levels. Since it's a read-only port, there has to be some way of recording
what we do to it. We have to save what we do with that port into _contrast
($c008). We have to check what that value is, see if it's maxed out or
at the minimum. Then we send the new contrast through port 2 and save
what we did to _contrast. The program
Contrast.asm
is an example of changing the contrast with the Up and Down keys.
Here's another routine that increases the contrast if possible.
_contrast =$c008 ;where contrast is stored contrast_port =2 ;port controlling contrast increase_contrast: ld hl,_contrast ;address of contrast ld a,(hl) ;get contrast cp 31 ;compare it to max ret z ;it was 31 so return inc a ;increase contrast ld (hl),a ;put back changes out (contrast_port),a ;update contrast ret
| Set | Reset | |
| Read: | Bit 3 - [ON] key was not pressed Bit 2 - Timer interrupt happened Bit 1 - LCD is on Bit 0 - [ON] interrupt happened |
Bit 3 - [ON] was pressed Bit 2 - Timer interrupt hasn't happened Bit 1 - LCD is off Bit 0 - [ON] interrupt hasn't happened |
| Write: | Bit 3 - Turn LCD off Bit 2 - Don't mask timer interrupts (200Hz) Bit 1 - LCD status on* Bit 0 - Don't mask [ON] key interrupts* |
Bit 3 - Turn LCD on Bit 2 - Mask timer interrupts (200Hz) Bit 1 - LCD status off Bit 0 - Mask [ON] key interrupts |
* Don't exit to TI-OS with bits 0 or 1 reset or the calculator will freeze.
The PressOn.asm program shows how to check for [ON] being pressed like this. More on this in the On-Off Section.
in a,(on_port) ;get status bit 3,a ;on's bit..reset if down call z,pressing ;[on] is being held ; down now so call ; 'pressing' routine
You can turn off the screen manually too. Note that this doesn't turn off the calculator, it merely quits refreshing the Video Memory to the screen. The TI86 will still be running in normal power mode, as opposed to low power mode when TI-OS turns if off. Details in the On-Off Section. Since the processor is executing this code fast, it will be turning on and off probably 50 times while you're pushing the [ON] button down and releasing it. You can try to slow down the processor some by having it check other stuff in the mean time or just doing other tasks instead of continually checking for the [ON] key being pressed.
turn_off:
ld a,%00000001
out (3),a ;turn off lcd
halt ;wait for [on]
ld a,%00000010
out (3),a ;turn on lcd
res onInterrupt,(iy+onFlags)
;turn off the flag so
;ti-os doesn't detect it too
ret
I can direct you to Randy Gluvna's
LinkRout.h or
ACZ's
copy Link86.asm.
With this routine, you will be able to send and
receive single bytes. I'm sorry for the inconvenience
this may have caused.
Port 4 - Power Mode
Port 4 is used for the the Power Mode mainly. It's either
in Normal Power Mode or Low Power Mode. This is all done
with bit 0. TI-OS puts the calculator in Low Power Mode
before shutting down to save battery life. If bit 0
is reset, it's in Low Power Mode; set is High Power Mode.
Here's how to check if it's in low power mode.
mode_port =4 ;port to check
power_mode:
in a,(mode_port) ;get status
bit 0,a ;check mode
jr z,in_low_power_mode ;is in low power mode
ret
Port 5 - ROM Pages
See Memory
and R_M Pages.
Port 6 - RAM Pages
See Memory
and R_M Pages.
Port 7 - Link Port
Port 7 is used for the link port. It can be used for
sound, memory expanders, or
sending/receiving information.
I haven't researched this area much. Check back sometime
because I've ordered a second TI86 to work with.