rs232 interupt on old ibm pc type machines

[Hul Tytus]

sci.electronics.design
rs232 interupt on old ibm pc type machines

Below are an rs232 initialization and a handler routine that work well on
later vintage ibm pc types, roughly 200 mc and above. The AT vintage types
however are a bust. The 8250 registers and the interupt mask register in the
interupt controller appear as expected in both cases.
Anyone have an idea what is missing for the older machines?

Hul

_____________________________________________________
; interupt enable bits
DATAIN equ 1 ; data availalbe
TRANEMP equ 2 ; transmit holding reg empty
RECLINE equ 4 ; receive line status
MODSTAT equ 8 ; modem status

ptype rsinit ; rsinit(port) -- port assumed 0 for now
; initialize interupt req #4 (int 0c) for rs232 line
push bx
push cx
push dx
push ds
mov ax, DDDTA ; base of data
mov ds, ax

mov dx, 0
call irsadd ; return port address for '0' port (com1)
inc dx
in al, dx
or al, DATAIN ; enable incoming data interupt
out dx, al

add dx, 3
in al, dx
or al, 8 ; set out2 bit in uart to enable interupts
out dx, al

push cs
pop cx
mov dx, offset rs4hand ; new address for irq 4 handler
; see below
push ds
mov bx, 0
mov ds, bx
mov bx, 2ch
cli
mov ax, [bx] ; read old address and
mov [bx], dx ; place the new one
add bx, 2
mov dx, [bx] ; ditto
mov [bx], cx
sti
pop ds
mov word ptr ds:[intcadd], ax
mov word ptr ds:[intcadd+2], dx ; the org address has been saved

mov dx, 21h ; interrupt control reg
in al, dx ; read current interrupt mask register
and al, 0FFh-10h ; allow interrupts from COM1
out dx, al

pop ds
pop dx
pop cx
pop bx
ret
rsinit endp

rs4hand proc near ; handler for interrupt #4
sti ;Allow interrupts ?
push ax
push bx
push dx
push ds
mov ax, DGROUP
mov ds, ax

mov dx, 20h ; System interrupt controller
mov al, 20h ; Reset interrupt pending
out dx, al ; Put back to system controller

mov dx, 0 ; assume port 0 -- ie COM1
call irsadd ; returns address for passed port
inc dx
inc dx ; point at interrupt id reg

in al, dx ; get interrupt type
test al, 1 ; any interrupt pending?
jnz rs4hnd1 ; no - return
cmp al, 4
jnz rs4hnd1
dec dx
dec dx
in al, dx
call rsinplc ; places al in recieved data buffer

rs4hnd1:
pop ds
pop dx
pop bx
pop ax
iret
rs4hand Endp

 

[Jasen Betts]

sci.electronics.design
rs232 interupt on old ibm pc type machines

Below are an rs232 initialization and a handler routine that work well on
later vintage ibm pc types, roughly 200 mc and above. The AT vintage types
however are a bust. The 8250 registers and the interupt mask register in the
interupt controller appear as expected in both cases.
Anyone have an idea what is missing for the older machines?

http://en.wikibooks.org/wiki/Serial_Programming/DOS_Programming

any help?

 

[[email protected]]

Thanks Jasen, I'll take a look.

Hul

any help?

 

[Tim Williams]

Don't see anything wrong offhand, but I don't remember the serial port so
well.

I have an XT-compatible if you'd like to test further back.

The BIOS, and DOS, have some serial drivers, but I don't remember if
interrupts are offered. It's pretty standard to work directly with the
serial hardware, so that doesn't matter much.

You should ask DOS to patch in the interrupt -- see INT 21h, AH = 25h.
That way if your program closes abruptly, DOS knows what to fix.

You can also further use DOS to install your own CTRL+BREAK handler (INT
23h) if occasional freezes are a possibility, as sometimes happens in
development.

BTW, which assembler are you using? I mostly use MASM, have you
considered it? Automatic stack frames is niiice. ;-)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com

sci.electronics.design
rs232 interupt on old ibm pc type machines

Below are an rs232 initialization and a handler routine that work well
on
later vintage ibm pc types, roughly 200 mc and above. The AT vintage
types
however are a bust. The 8250 registers and the interupt mask register in
the
interupt controller appear as expected in both cases.
Anyone have an idea what is missing for the older machines?

Hul

_____________________________________________________
; interupt enable bits
DATAIN equ 1 ; data availalbe
TRANEMP equ 2 ; transmit holding reg empty
RECLINE equ 4 ; receive line status
MODSTAT equ 8 ; modem status

ptype rsinit ; rsinit(port) -- port assumed 0 for now
; initialize interupt req #4 (int 0c) for rs232 line
push bx
push cx
push dx
push ds
mov ax, DDDTA ; base of data
mov ds, ax

mov dx, 0
call irsadd ; return port address for '0' port (com1)
inc dx
in al, dx
or al, DATAIN ; enable incoming data interupt
out dx, al

add dx, 3
in al, dx
or al, 8 ; set out2 bit in uart to enable interupts
out dx, al

push cs
pop cx
mov dx, offset rs4hand ; new address for irq 4 handler
; see below
push ds
mov bx, 0
mov ds, bx
mov bx, 2ch
cli
mov ax, [bx] ; read old address and
mov [bx], dx ; place the new one
add bx, 2
mov dx, [bx] ; ditto
mov [bx], cx
sti
pop ds
mov word ptr ds:[intcadd], ax
mov word ptr ds:[intcadd+2], dx ; the org address has been saved

mov dx, 21h ; interrupt control reg
in al, dx ; read current interrupt mask register
and al, 0FFh-10h ; allow interrupts from COM1
out dx, al

pop ds
pop dx
pop cx
pop bx
ret
rsinit endp

rs4hand proc near ; handler for interrupt #4
sti ;Allow interrupts ?
push ax
push bx
push dx
push ds
mov ax, DGROUP
mov ds, ax

mov dx, 20h ; System interrupt controller
mov al, 20h ; Reset interrupt pending
out dx, al ; Put back to system controller

mov dx, 0 ; assume port 0 -- ie COM1
call irsadd ; returns address for passed port
inc dx
inc dx ; point at interrupt id reg

in al, dx ; get interrupt type
test al, 1 ; any interrupt pending?
jnz rs4hnd1 ; no - return
cmp al, 4
jnz rs4hnd1
dec dx
dec dx
in al, dx
call rsinplc ; places al in recieved data buffer

rs4hnd1:
pop ds
pop dx
pop bx
pop ax
iret
rs4hand Endp