AT89C2051 Timers

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I am considering this MCU for a project but the info from Atmel leaves
a lot to be desired.  In looking at the Intel MCS-51 info it would
appear that if one is going to use the serial interface that one of
the timers must be used to generate the baud rate.  True?  What is the
clock rate of the timers?  Can it be adjusted (programmed)?

Re: AT89C2051 Timers
Brad schrieb:
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Yes, at least if you need some useful baud rate.

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The timer division ratio is of course programmable.
However, you need to consider that the crystal frequency is
first divided by 12, and the UART further divides by 16.
So your crystal frequency should be a multiple of 16 x 12 x
your maximum baud rate. This leads to those seemingly odd
crystals you surely have seen before.

Practically, most of the time a 11.0592 MHz crystal is used,
which is good for up to 19200 Bd (timer divides by 3).
You could also use 7.3728 or 14.7456 MHz, or 22.1184 MHz,
or ....

And take care to set the MSB in PCON, otherwise your UART clock
is further divided by two.

Dipl.-Ing. Tilmann Reh
Autometer GmbH Siegen - Elektronik nach Maß.
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Re: AT89C2051 Timers

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Yes, you use one of the timers.

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You may also want to look at an Atmel AVR as well.

                    AT89C2051    ATtiny2313
Flash            2kB                  2kB
RAM            128                  128
EEPROM     -                      128
Pins              20                      20
Freq             24                      16
MIPS            2                       13
8 bit timer       -                       1
16 bit timer     1                       1
BAUD timer   1                     in UART
UART            1                      1
ISP                 -                      yes                        ISP =
In System Programming
Watchdog       -                      yes
R/C osc          -                      yes
BrownOut       -                     yes

Easier to program and free tools.

Best Regards,
Ulf Samuelsson
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Re: AT89C2051 Timers
there are very similar microcontrollers out there that do not need
touse a timer because they use a baudrate generator. For example the
LPC900 series of Philips does not need an external clock (internal
oscillator) and can generate all baudrates up to 115200 from this
internal oscillator with the integrated baudraget generator. You will
have T0 and T1 for your application and even a Real Time clock.
Possible catch: The LPC900 family does not run @ 5V, just between 2.4V
and 3.6V

you can check Keil's website:
or Philips:
sorry for that long URL, "typical big company"
or some very usefull information is here:

Cheers, Schwob (Brad) wrote in message
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