Slow AMBA Peripherals
13-12
GMS30C7201 Data Sheet
Bit 2:
This bit specifies the number of Stop bits transmitted and received in
each serial character. If bit 2 is a logic 0, one Stop bit is generated in
the transmitted data. If bit 2 is a logic 1 when a 5-bit word length is
selected via bits 0 and 1, one and a half Stop bits are generated. If bit 2
is a logic 1 when either a 6-, 7- or 8-bit word length is selected, two
Stop bits are generated. The Receiver checks the first Stop-bit only,
regardless of the number of Stop bits selected.
This bit is the Parity Enable bit. When bit 3 is a logic 1, a Parity bit is
generated (transmit data) or checked (receive data) between the last
data word bit and Stop bit of the serial data. (The Parity bit is used to
produce an even or odd number of 1s when the data word bits and the
Parity bit are summed.)
This bit is the Even Parity Select bit. When bit 3 is a logic 1 and bit 4 is
a logic 0, an odd number of logic 1s is transmitted or checked in the
data word bits and Parity bit. When bit 3 is a logic 1 and bit 4 is a
logic 1, an even number of logic 1s is transmitted or checked.
This bit is the Stick Parity bit. When bits 3, 4 and 5 are logic 1 the Parity
bit is transmitted and checked as a logic 0. If bits 3 and 5 are 1 and bit
4 is a logic 0 then the Parity bit is transmitted and checked as a logic 1.
If bit 5 is a logic 0 Stick Parity is disabled.
This bit is the Break Control bit. It causes a break condition to be
transmitted to the receiving UART. When it is set to a logic 1, the serial
output (
SOUT
)is forced to the Spacing (logic 0) state. The break is
disabled by setting bit 6 to a logic 0. The Break Control bit acts only on
SOUT
and has no effect on the transmitter logic.
Note: This feature enables the CPU to alert a terminal in a computer
communications system. If the following sequence is followed, no
erroneous or extraneous characters will be transmitted because of the
break.
This bit is the Divisor Latch Access Bit (DLAB). It must be set HIGH
(logic 1) to access the Divisor Latches of the Baud Generator during a
Read or Write operation. It must be set LOW (logic 0) to access the
Receiver Buffer, the Transmitter Holding Register or the Interrupt
Enable Register.
Bit 3:
Bit 4:
Bit 5:
Bit 6:
Bit 7:
Programmable Baud Generator
The UART contains a programmable Baud Generator that is capable of taking any clock
input from DC to 8.0MHz and dividing it by any divisor from 2 to 2
16
–
1. 4MHz is the
highest input clock frequency recommended when the divisor=1. The output frequency
of the Baud Generator is 16 x the Baud [divisor # = (frequency input) / (baud rate x 16)].
Two 8-bit latches store the divisor in a 16-bit binary format. These Divisor Latches must
be loaded during initialization to ensure proper operation of the Baud Generator. Upon
loading either of the Divisor Latches, a 16-bit Baud counter is immediately loaded.
Table 13-8: Baud rates
on page 13-13 provide decimal divisors to use with a crystal
frequency of 3.6864MHz. For baud rates of 38400 and below, the error obtained is
minimal. The accuracy of the desired baud rate is dependent on the crystal frequency
chosen. Using a divisor of zero is not recommended.