COP8AME9_14 Datasheet, PDF (57/102 Pages) Texas Instruments – COP8AME9 8-Bit CMOS Flash Microcontroller with 8k Memory, Dual Op Amps, Virtual EEPROM, Temperature Sensor, 10-Bit A/D and Brownout Reset

COP8AME9, COP8ANE9
www.ti.com
SNOS930F – MARCH 2001 – REVISED MARCH 2013
Where:
BR is the Baud Rate
F_C is the crystal frequency
N is the Baud Rate Divisor (Table 21)
P is the Prescaler Divide Factor selected by the value in the Prescaler Select Register (Table 22)
Note: In the Synchronous Mode, the divisor 16 is replaced by two.
Example:
Asynchronous Mode:
Crystal Frequency = 5 MHz
Desired baud rate = 19200
Using the above equation N × P can be calculated first.
N × P = (5 x 10⁶ x 2)/(16 x 19200) = 32.552
Now 32.552 is divided by each Prescaler Factor (Table 22) to obtain a value closest to an integer. This factor
happens to be 6.5 (P = 6.5).
N = 32.552/6.5 = 5.008 (N = 5)
The programmed value (from Table 21) should be 4 (N - 1).
Using the above values calculated for N and P:
BR = (5 x 10⁶ x 2)/(16 x 5 x 6.5) = 19230.769
error = (19230.769 - 19200) x 100/19200 = 0.16%
Figure 26. USART BAUD Clock Divisor Registers
EFFECT OF HALT/IDLE
The USART logic is reinitialized when either the HALT or IDLE modes are entered. This reinitialization sets the
TBMT flag and resets all read only bits in the USART control and status registers. Read/Write bits remain
unchanged. The Transmit Buffer (TBUF) is not affected, but the Transmit Shift register (TSFT) bits are set to
one. The receiver registers RBUF and RSFT are not affected.
The device will exit from the HALT/IDLE modes when the Start bit of a character is detected at the RDX (L3) pin.
This feature is obtained by using the Multi-Input Wake-up scheme provided on the device.
Before entering the HALT or IDLE modes the user program must select the Wake-up source to be on the RDX
pin. This selection is done by setting bit 3 of WKEN (Wake-up Enable) register. The Wake-up trigger condition is
then selected to be high to low transition. This is done via the WKEDG register (Bit 3 is one).
If the device is halted and crystal oscillator is used, the Wake-up signal will not start the chip running immediately
because of the finite start up time requirement of the crystal oscillator. The IDLE timer (T0) generates a fixed
(256 t_C) delay to ensure that the oscillator has indeed stabilized before allowing the device to execute code. The
user has to consider this delay when data transfer is expected immediately after exiting the HALT mode.
Copyright © 2001–2013, Texas Instruments Incorporated
Submit Documentation Feedback
57
Product Folder Links: COP8AME9 COP8ANE9