BBS: Inland Empire Archive
Date: 08-07-92 (13:57) Number: 62
From: JEAN CREPEAU Refer#: NONE
To: JAMES VAHN Recvd: NO
Subj: Uevent Conf: (2) Quik_Bas
In a message to ALL, JAMES VAHN wrote:
JV=> Could someone explain the use of QB4.5's ON UEVENT GOSUB ...? I wish
to run a background task and think that's the ticket. I'd like to tap
into INT 8 or better yet set up the 8255 PPI and the 8253 timer.
Actually would like to see both methods.
The ON ... GOSUB is called a trap. You can force QuickBASIC to make
an automatic GOSUB on certain events. For instance, you can trap a key
sequence, the timer or the joystick.
On timer(1) gosub timetrap
(cont...)
timetrap:
print "Another second just passed"
return
The trap will be executed once every second.
The only problem with the QB traps is that they check for the
events between instructions (compiled with /v) or between lines (/w). If
you INPUT something, no trap will be executed until the instruction is
finished (i.e. the user presses enter).
You could try to program the INT 8, but making an interrupt
subroutine with QuickBASIC is not a good idea. QB doesn't provide any mean
to do that anyway.
If you want to program the PPI or CTC, it's easy... Here are the
internal registers of the PPI and the CRC:
PPI+0: Port A (The adress is 60h on XT)
PPI+1: Port B (The adress is 61h on XT)
PPI+2: Port C (The adress is 62h on XT)
PPI+3: Control (The adress is 63h on XT)
b7: Always 1
b6-b5: Port A mode (00=mode 0, 01=mode 1, 10=mode 2)
b4: Port A dir (0=Output, 1=Input)
b3: Port C, high nibble dir (0=Out,1=In)
b2: Port B mode (0=mode 0, 1=mode 1)
b1: Port B dir (0=Output, 1=Input)
b0: Port C, low nibble dir (0=Out, 1=In)
Mode 0 is generally used
CTC+0: Channel 0 counter I/O (adress=40h)
CTC+1: Channel 1 counter I/O (adress=41h)
CTC+2: Channel 2 counter I/O (adress=42h)
CTC+3: Control (adress=43h)
b7-b6: counter select (00=0, 01=1, 10=2, 11=illegal)
b5-b4: 00: Temp. freeze counter for reading
01: Read/write the LSB
10: Read/write the MSB
11: Read/write the LSB, then the MSB
b3-b1: 000: Mode 0 (restart to count when a new counter is loaded)
001: Mode 1 (restart to count when the trigger activated)
x10: Mode 2 (automatic restart when counter is finished)
x11: Mode 3 (like 2, but generates a square signal=>sound)
100: Mode 4 (like 0, but generates a pulse)
101: Mode 5 (like 1, but generates a pulse)
b0: counter type (0=16-bit, 1=BCD)
Normally, all input clocks for the three timers are connected to a
1.19047 MHz clock. Channel 0 is used for DOS internal clock. Channel 1 is
used for RAM refresh. And channel 2 is used for sound generation.
For instance if you want to program channel 2 for sound:
Out 43h,10110110
(Program channel 2, LSB/MSB, mode 3 in 16-bit)
Counter&=1190470/Freq
MSB%=int(Counter&/256)
LSB%=Counter& and 255
Out 42h,LSB%
Out 42h,MSB%
Out 61h,In(61h) or 3
The last line is used to activate the speaker with the channel 2,
by setting bits 0 and 1 of PPI Port B to 1.
Jean
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* Origin: INTERACESS Montreal (QC) Canada (514) 528-1415 (1:167/280)
