GR740-UM-DS, Nov 2017, Version 1.7
323
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GR740
23
UART Serial Interfaces
23.1
Overview
Two UART interfaces are provided for serial communications. Each UART supports data frames with
8 data bits, one optional parity bit and one stop bit. To generate the bit-rate, each UART has a pro-
grammable 20-bit clock divider. Two FIFOs are used for data transfer between the APB bus and
UART. Hardware flow-control is supported through RTSN/CTSN hand-shake signals.
23.2
Operation
23.2.1 Transmitter operation
The transmitter is enabled through the TE bit in the UART control
register. Data that is to be trans-
ferred is stored in the 16-byte FIFO by writing to the data register. When ready to transmit, data is
transferred from the transmitter FIFO to the transmitter shift register and converted to a serial stream
on the transmitter serial output pin. The core automatically sends a start bit followed by eight data
bits, an optional parity bit, and one stop bit (figure 40). The least significant bit of the data is sent first.
Following the transmission of the stop bit, if a new character is not available in the transmitter FIFO,
the transmitter serial data output remains high and the transmitter shift register empty bit (TS) will be
set in the UART status register. Transmission resumes and the TS is cleared when a new character is
Figure 39.
Block diagram
RXD
TXD
CTSN
RTSN
Receiver shift register
Transmitter shift register
APB
Serial port
Controller
8*bitclk
Baud-rate
generator
Transmitter FIFO
Receiver FIFO
Figure 40.
UART data frames
Start D0
Stop
D6
D5
D4
D3
D2
D1
D7
Start D0
D6
D5
D4
D3
D2
D1
D7
Stop
Parity
Data frame, no parity:
Data frame with parity: