Group Members,
Beginning in the days of the 1200 bps DPSK modem, clock crystals were
specified to .01% to allow the demodulator at the receiving end to
recover the clock in the data-stream and lock to it. The asynchronous
serial port attached to the modem needed to be no more accurate than 1%,
as the modem included an async-to-sync converter that would strip every
eighth stop bit, if necessary, to reduce the incoming data rate to the
modem rate. The sync-to-async converter in the receiving modem
re-inserted the missing stop bits. The case of incoming data under-speed
was handled in a similar manner.
The older FSK modems were much different. They would shift from mark to
space tones at the data-rate you used. The filters and tone spacings
were typically optimized for 300 bps, but across town, 450 bps was
achievable.
Peter Putnam
On 7/2/2010 6:17 PM, Bob Camp wrote:
Hi
A lot depends on just what you worry about. Most clock specs for serial com are
in the 0.01 to 0.1% range.
Bob
On Jul 2, 2010, at 9:02 PM, Chuck Harris wrote:
The PIC's internal silicon clock is better than 1% over the entire industrial
voltage and temperature range. They are accurate enough.
-Chuck Harris
Bob Camp wrote:
Hi
I believe he's using the internal clock on the PIC. It's not super accurate,
so running a lot of data can be an issue.
Bob
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Stanley Reynolds
Sent: Friday, July 02, 2010 3:41 PM
To: [email protected]
Subject: [time-nuts] Pictic II mods
Looking at Richard's code in PICTICII.ASM :
bsf TXSTA,BRGH ;set USART hi speed mode
movlw D'51' ;set async rate at 9600 baud (51. for
8
MHz int, BRGH=1)
movwf SPBRG
Then '25' would be 19,200 baud
and '12' would be 38,400 baud
Need to test this but could be a way to get more data out.
Stanley
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