DS80C320-ECD DALLAS [Dallas Semiconductor], DS80C320-ECD Datasheet - Page 144

• Manufacturer Part Number: DS80C320-ECD
• Description: High-Speed Microcontroller User Guide
• Manufacturer: DALLAS [Dallas Semiconductor]

Mode 1 or 3
These asynchronous modes are commonly used for communication with PCs, modems, and other similar
interfaces. The baud rates are programmable using the oscillator input and 16-bit Timer 2 or 8-bit Timer
1. The respective timer is placed in auto-reload mode. Each time the timer reaches its rollover condition
(FFFFh -Timer 2 or FFh - Timer 1), a clock is sent to the baud rate circuit. This clock is then divided by
16 to generate the exact baud rate. For Serial Port 0, either Timer 1 or 2 can be used to generate baud
rates. Note that there are difdivider regisferences between the timers when used as baud rate generators.
Serial Port 1 can use Timer 1 as a baud rate generator. Thus in Mode 1 or 3, the two serial ports can
run at the same frequency if Timer 1 is used for both, but different frequencies if both timers are used.
Also note that the user can determine the speed at which Timer 1 runs (4 clocks or 12 clocks). In most
cases, 12 clocks will be used for baud rate generation. Timer 2 runs from a 2 clock scheme when used for
baud rate generation. This is compatible with the 80C32.
The baud rates for Mode 1 or 3 are given by these formulas.
Serial Port 0 or 1
Serial Port 0
To use Timer 1 as the baud rate generator, it is commonly put into the 8-bit auto-reload mode. In this
way, the CPU is not involved in baud rate generation. Note that the timer interrupt should not be enabled.
In the 8-bit auto-reload mode (Timer 1 Mode 2), the reload value is stored in TH1. Thus the combination
of crystal frequency and TH1 determine the baud rate. The complete formula is as follows.
Note that the 12 in the denominator can be changed to a 4 as determined by the Timer selection (T1M;
CKCON.4). This formula provides the derived baud rate for a given TH1 and crystal. Most users already
know what baud rate is desired and want the timer reload value. Thus the equation solves as follows,
when T1M=0.
Note that the most common application is to use Timer 1 in 8-bit auto-reload mode as a timer. It can
actually be used in any mode and can also be configured as a counter.
To use Timer 2 as baud rate generator for Serial Port 0, the Timer is configured in auto-reload mode.
Then either TCLK or RCLK bit (or both) are set to a logic 1. TCLK = 1 selects Timer 2 as the baud rate
generator for the transmitter and RCLK = 1 selects Timer 2 for the Thus Serial Port 0 can have the
transmit and receive operating at different baud rates by choosing 1 for one data direction and Timer 2 for
Mode 1, 3 baud rate =
Mode 1, 3 baud rate =
Mode 1, 3 baud rate =
TH1 = 256 -
2
SMOD_x
Timer 2 Overflow
2
2
32* Baud Rate
* Oscillator Frequency
SMOD_x
SMOD_x
32
32
16
144 of 175
*
*
Timer 1 Overflow
Oscillator Frequency
12 * (256 - TH1)
High-Speed Microcontroller User’s Guide