schimpf@utah-cs.UUCP (James Schimpf) (08/09/85)
<HELP -- >
We are building a small system here based on an INTEL 80186
and are trying to use one of the on chip timers to generate a baud
rate clock. The '186 is running at 8 MHz (16 MHz crystal) and we
are trying to use TIMER 0 on the chip as the generator for a x16
clock for a 9600 baud serial line.
Our processor registers (TIMER, DMA, memory control etc.)
are mapped to memory starting at F0000H. Our code does the
following:
Set location F0052H (Timer 0 A register) to 0DH
Set location F0056H (Timer 0 cntl) to C001H
and a continuous ~150Khz clock is generated.
The above is pretty much a copy of what is done in the INTEL
application note AP 186. It does work ONCE. It will continue to run
for hours this way but after the chip is warmed up if it is RESET or
powered down and back up again this timer won't work again. Also at
this point (i.e. timer not working) the only count value that will
make it work is a 1 in the TIMER A register. Using this you can
generate a 4 MHz clock signal. From the design notes on the chip
this frequency is impossible (2 MHz max with a 8 MHz clock).
Ah ha, you say its a bad chip ! Well no, we have exactly the
same problem on 4 different chips (2 B step chips and 2 C step chips).
(The B & C stuff means something to the INTEL folk)
The processors all seem to run OK as the above messing with
timer registers is all done via a monitor/debugger running using the
chip. And this debugger never stops or even gliches during the
testing.
We have read the manuals and the AP note so we think we are
doing the right thing but is there some secret to this ? That we
can make them work when the chip is cold shows we are doing some of
the right stuff but is there something else ?
Any suggestions or war stories would be appreciated. Mail
it to me or put it on the net if you think it is of general
interest.
--Jim Schimpf U. of U. CS Dept
ARPA: schimpf@utah-20
Net Mail: {ihnp4,decvax,seismol!utah-cs!schimpflarry@kitty.UUCP (Larry Lippman) (08/11/85)
> We are building a small system here based on an INTEL 80186 > and are trying to use one of the on chip timers to generate a baud > rate clock. The '186 is running at 8 MHz (16 MHz crystal) and we > are trying to use TIMER 0 on the chip as the generator for a x16 > clock for a 9600 baud serial line. > Our processor registers (TIMER, DMA, memory control etc.) > are mapped to memory starting at F0000H. Our code does the > following: > Set location F0052H (Timer 0 A register) to 0DH > Set location F0056H (Timer 0 cntl) to C001H > The above is pretty much a copy of what is done in the INTEL > application note AP 186. It does work ONCE. It will continue to run > for hours this way but after the chip is warmed up if it is RESET or > powered down and back up again this timer won't work again. ... Simple problem, simple solution - I believe... Timer 0 and timer 1 both have INPUT pins (20 and 21, respectively) which ALWAYS do something. If you have EXT bit as 1, then these pins supply the external clock; if EXT is 0 and you are using the internal clock (as you are), then these pins function as a gate or reset depending upon the value of RTG bit. Since you have RTG as 0, and based upon your application, you must have pin 20 logically HIGH. I betcha it's floating in the breeze... One other piece of advice I have learned the hard way: Don't take the Intel APP notes as gospel! +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ | Larry Lippman @ Recognition Research Corp., Clarence, New York | | UUCP {decvax,dual,rocksanne,rocksvax,watmath}!sunybcs!kitty!larry | | {rice,shell}!baylor!/ | | VOICE 716/741-9185 syr!buf!/ | | TELEX {via WUI} 69-71461 ansbak: ELGECOMCLR | | | | "Have you hugged your cat today?" | +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++