MON51: Baud Rates

Information in this article applies to:

• C51 Version 5.50a and later

QUESTION

What baud rates does the MON51 target monitor support?

ANSWER

The MON51 target monitor works at any baud rate. However, depending on the crystal frequency of your target microcontroller, you may be limited in the baud rates that your hardware supports.

For a standard 8051-compatible part at 12.000 MHz, the following table lists the actual baud rates for the indicated timer reload values:

Reload   Desired       Actual
Value   Baud Rate    Baud Rate     Difference
 FFh                   31250
 FEh                   15625
 FDh      9600         10416.66      +8%
 FCh      9600          7812.5       -22%
 FBh                    6250
 FAh                    5208.33
 F9h      4800          4464.28      -7%
 F8h                    3906.25

 F3h      2400          2403.84      +0.1%
 F2h                    2232.14

 E6h      1200          1201.92      +0.08%

 98h       300          300.48       +0.1%

Different serial devices provide flexibility in supporting non-exact baud rates. However, a good rule of thumb is +1%/-2% for deviations from the baud rate. Therefore, the only baud rates from the above table that are reasonable are 2400, 1200, and 300 baud (for 12MHZ devices).

You should also be aware of slew rates when using a MAX232 or similar driver. The slew rates may also affect the speed you can achieve.

SEE ALSO

• C51: Calculating Baud Rates for the 8051 Serial Port
• MON51: Connection to Target System Lost
• MON51: Configuring for Target
• MON51: Testing Von Neumann Memory Areas
• MON51: MONITOR DATA AREA

Last Reviewed: Thursday, February 25, 2021