ST92196A STMicroelectronics, ST92196A Datasheet - Page 195

• Manufacturer Part Number: ST92196A
• Description: 8/16-bit Mcu For Tv Applications With Up To 96k Rom, On-screen-display And 1 Or 2 Data Slicers
• Manufacturer: STMicroelectronics

SERIAL COMMUNICATIONS INTERFACE (Cont’d)
8.11.4 Clocks And Serial Transmission Rates
The communication bit rate of the SCI transmitter
and receiver sections is provided from the internal
Baud Rate Generator divided by 16. x
Baud Rate Generator. The internal Baud Rate
Generator consists of a 16-bit programmable di-
vide by “N” counter which can be used to generate
the transmitter and/or receiver clocks. The mini-
mum baud rate divisor is 2 and the maximum divi-
sor is 2
With INTCLK running at 20MHz or 10MHz, a max-
imum bit rate of 625 KBaud or 312.5K Baud re-
spectively is possible.
WARNING: Programming the baud rate divider to
0 or 1 will stop the divider.
The output of the Baud Rate generator has a pre-
cise 50% duty cycle. INTCLK (and therefore the
MCU Xtal) should be chosen to provide a suitable
frequency for division by the Baud Rate Generator
to give the required transmit and receive bit rates.
Suitable INTCLK frequencies and the respective
divider values for standard Baud rates are shown
in
8.11.5 SCI Initialization Procedure
Writing to either of the two Baud Rate Generator
Registers immediately disables and resets the SCI
195/268
- SERIAL COMMUNICATIONS INTERFACE (SCI)
Table
16
41.
-1.
baud rate generator, as well as the transmitter and
receiver circuitry.
After writing to the second Baud Rate Generator
Register, the transmitter and receiver circuits are
enabled. The Baud Rate Generator will load the
new value and start counting.
To initialize the SCI, the user should first initialize
the most significant byte of the Baud Rate Gener-
ator Register; this will reset all SCI circuitry. The
user should then initialize all other SCI registers
(SICR/SOCR included) for the desired operating
mode and then, to enable the SCI, he should ini-
tialize the least significant byte Baud Rate Gener-
ator Register.
'On-the-Fly' modifications of the control registers'
content during transmitter/receiver operations, al-
though possible, can corrupt data and produce un-
desirable spikes on the I/O lines. Furthermore,
modifying the control registers' content without
reinitialising the SCI circuitry (during stand-by cy-
cles, waiting to transmit or receive data) must be
kept carefully under control by software to avoid
spurious data being transmitted or received.