Digi NS9215 - Manual (Page 388)

S E R I A L C O N T R O L M O D U L E : U A R T
Hardware-based flow control
388 Hardware Reference NS9215
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H a r d w a r e - b a s e d f l o w c o n t r o l
The UART module provides expanded functionality for hardware-based flow control.
The RTS signal normally indicates the state of the receive FIFO. The CTS signal
normally halts the transmitter. With this UART module, the RI, CTS, DCD, or DSR
signals can halt the transmitter. Program these features using the HWFLOW bits in
the Wrapper Configuration register.
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C h a r a c t e r - b a s e d f l o w c o n t r o l ( X O N / X O F F )
Traditional character-based flow control requires the processor to match the flow
control characters and control the transmitter accordingly. This UART module
performs the character matching function in hardware and automatically updates
the state of the transmitter, which allows character-based flow control to achieve
the same response time as hardware-based flow control.
Example
configuration
Configure the character-based flow control using at least two Receive Character
Match registers and the Receive Character-Based Flow Control register. This table
shows a sample configuration for a system transferring 8 data bits per character.
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F o r c e d c h a r a c t e r t r a n s m i s s i o n
UART provides a mechanism in which you can bypass data in the transmit FIFO with
a specific character. The specified character is transmitted after the current
Control register Field Value Comment
Receive Character Match Control
Register 0 ENABLE 1 Enable character match
MASK 0x00 Mask bits
DATA 0x7e Define character
Receive Character Match Control
Register 1 ENABLE 1 Enable character match
MASK 0x00 Mask bits
DATA 0x81 Define character
Receive Character-Based Flow
Control register FLOW0 0x2 XON when matched
FLOW1 0x3 XOFF when matched