Hardware Reference
In-Depth Information
Table 9-1.
RS-232 Parity Settings
Parity
X
Notes
None
N
No parity bit
Even
E
1 if even number of data 1-bits
Odd
O
1 if odd number of data 1-bits
Mark
M
Always at mark level (1)
Space
S
Always at space level (0)
Stop Bit(s)
Asynchronous communication requires synchronizing the receiver with the transmitter.
For this reason, 1 or more stop bits exist so that the receiver can synchronize with the
leading edge of the next start bit. In effect, each stop bit followed by a start bit provides
built-in synchronization.
Many UARTs support 1, 1.5, or 2 stop bits. The Broadcom SoC supports 1 or 2 stop
bits only. The use of 2 stop bits was common for teletypewriter equipment and probably
rarely used today. Using 1 stop bit increases the overall data throughput. Table
9-2
summarizes the stop-bit configurations.
Table 9-2.
Stop-Bit Configuration
Stop Bits
Description
1
1 stop bit
1.5
1.5 stop bits (†)
2
2 stop bits
†Unsupported by the Raspberry Pi
Baud Rate
The
baud rate
is calculated from bits per second, which includes the start, data, parity,
and stop bits. A link using 115200 baud, with no parity and 1 stop bit, provides the
following data byte rate:
B
D
rate
=
sdpS
+++
115200
1801
11 52, ytes/sec
=
+++
=
