XR17C154 Datasheet, PDF (46/62 Pages) Exar Corporation – 5V PCI BUS QUAD UART

XR17C154
5V PCI BUS QUAD UART
áç
REV. 1.3.0
EFR[4]: Enhanced Function Bits Enable
Enhanced function control bit. This bit enables the functions in IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and
MCR bits 5-7 to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the
new values. This feature prevents legacy software from altering or overwriting the enhanced functions once
set. Normally, it is recommended to leave it enabled, logic 1.
• Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and MCR
bits 5-7 are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, FCR bits 4-5, and
MCR bits 5-7 are set to a logic 0 to be compatible with the industry standard 16550 (default).
• Logic 1 = Enables the enhanced functions. When this bit is set to a logic 1 all enhanced features are
enabled.
EFR[5]: Special Character Detect Enable
• Logic 0 = Special Character Detect Disabled (default).
• Logic 1 = Special Character Detect Enabled. The UART compares each incoming receive character with
data in Xoff-2 register. If a match exists, the received data will be transferred to FIFO and ISR bit-4 will be set
to indicate detection of the special character. Bit-0 corresponds with the LSB bit for the receive character. If
flow control is set for comparing Xon1, Xoff1 (EFR [1:0]=’10’) then flow control and special character work
normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]=’01’) then flow control works
normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character
interrupt.
TABLE 18: SOFTWARE FLOW CONTROL FUNCTIONS
TX S/W FLOW CONTROL
RX S/W FLOW CONTROL
EFR BIT-3
CONT-3
EFR BIT-2
CONT-2
EFR BIT-1
CONT-1
EFR BIT-0
CONT-0
SOFTWARE FLOW CONTROL FUNCTIONS
0
0
X
X
No transmit flow control
0
1
X
X
Transmit Xon2, Xoff2
1
0
X
X
Transmit Xon1, Xoff1
1
1
X
X
Transmit Xon1 and Xon2, Xoff1 and Xoff2
X
X
0
0
No receive flow control
X
X
0
1
Receiver compares Xon2, Xoff2
X
X
1
0
Receiver compares Xon1, Xoff1
0
1
1
1
Transmit Xon2, Xoff2
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1
0
1
1
Transmit Xon1, Xoff1
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
0
0
1
1
No transmit flow control
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
1
1
1
1
Transmit Xon1 and Xon2, Xoff1 and Xoff2
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
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