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Membership Card Super Monitor auto-baud maximum rates #MembershipCard #Serial #simulator


Ham Radio
 

Today, I experimented with various 1802 CPU  clock speeds using Chuck’s MCSMP20A monitor.

Clock         Maximum auto-baud  rate on serial port (in bps)
====.        =========
1.00  MHz.  1200
1.79  MHz.  9600
2.00  MHz.  2400
3.00 MHz.   4800
3.58 MHz.   9600
4.00 MHz.   4800

So, the best  bang for the buck is a TV colour burst XTAL, 3.58 MHz.  These cost about $1.00.  You get twice the CPU speed versus a 1.79 MHz ceramic resonator along  with a 9600 baud serial rate.

With real hardware, I did not need to add the 20pf caps to the 1802 oscillator circuit  (when I used  a real XTAL versus a ceramic resonator)  - your mileage may vary.  1.0 MHz and 3.0 MHz values were obtained  using the Emma emulator, not real hardware.

NOTE:  Some 1802 programs that use timing loops may not behave properly when using different clock speeds.


Regards,
Bernie Murphy


Bob Kay
 

I can confirm the 3.58/9600 baud, I was running just that for a while. I also tried 1, 2 and 4 MHz but honestly I forget which speeds I could get with which frequency.  One oddment I discovered is that my system would work at 9600 baud with a 1.8432 MHz oscillator, but wouldn't work with a 3.6864 MHz oscillator.  Note that 3.6864 is exactly double 1.8432, so it *should* have worked and the CPU chip in question handles 5MHz just fine so it's not an overclocking problem.


Lee Hart
 

Ham Radio wrote:
Today, I experimented with various 1802 CPU clock speeds using Chuck’s
MCSMP20A monitor.

Clock Maximum auto-baud rate on serial port (in bps)
====. =========
1.00 MHz. 1200
1.79 MHz. 9600
2.00 MHz. 2400
3.00 MHz. 4800
3.58 MHz. 9600
4.00 MHz. 4800

So, the best bang for the buck is a TV colour burst XTAL, 3.58 MHz.
These cost about $1.00. You get twice the CPU speed versus a 1.79 MHz
ceramic resonator along with a 9600 baud serial rate.
Interesting! The only odd result is that 9600 baud works for me at 4 MHz.

Chuck wrote his code to treat 9600 at 1.78 MHz as a special case. It does not auto-baud this rate; it just sets a fixed delay constant.

With real hardware, I did not need to add the 20pf caps to the 1802
oscillator circuit (when I used a real XTAL versus a ceramic
resonator) - your mileage may vary. 1.0 MHz and 3.0 MHz values were
obtained using the Emma emulator, not real hardware.
The 20pF capacitors help the oscillator start reliably, and make it run closer to the frequency of the crystal. Without them, there is a possibility of the oscillator running on some harmonic of its marked frequency (like a 1 MHz crystal oscillating at 3 MHz).

Some 1802 programs that use timing loops may not behave properly
when using different clock speeds.
Right! A faster clock speeds up *all* time delays. This could make a game more enjoyable; or make it unplayable.

Lee Hart

--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com


Ham Radio
 

I also tested at 6 MHz on an 1802ACE processor and 9600 bps works at this clock rate as well. Quite impressive at 6 MHz.

At 7 MHz, the 1802ACE system is unstable with VDD at 5.0 volts — no surprise here based on previous posts regarding various clock rates supported by the 1802.
--
Regards,
Bernie Murphy