Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 112)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
112 of 158
ADDENDUM TO SECTION 12: SERIAL I/O
The serial ports of the DS80C390’s Ax and Bx versions operate the same as those described in the High-
Speed Microcontroller User’s Guide
. Revision C3 and later devices will change the operation of serial
port 1 as follows.
When using serial port 1, it should be noted that setting either the RCLK or TCLK bit, used to select
timer 2 as the clock source for serial port 0, doubles the respective receive or transmit baud rate of serial
port 1. When the RCLK bit is set, the clock circuitry assumes the serial port 1 baud-rate double bit
(WDCON.7) is 0 for the purposes of calculating the serial port receiver baud rate. This is also true for the
TCLK bit and calculating the serial port transmitter baud rate.
In almost all implementations, RCLK and TCLK are set at the same time. If this is the case, then simply
calculate a new reload value for serial port 1 corresponding to a baud rate that is half the desired value.
This feature halves the doubled baud rate, allowing serial port 1 to operate at the desired baud rate for
both transmit and receive operations.