XR16L651 Datasheet, PDF (36/56 Pages) Exar Corporation – 2.25V TO 5.5V UART WITH 32-BYTE FIFO

XR16L651
2.25V TO 5.5V UART WITH 32-BYTE FIFO
EFR[3:0]: Software Flow Control Select
Combinations of software flow control can be selected by programming these bits.
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REV. 1.3.0
TABLE 12: SOFTWARE FLOW CONTROL FUNCTIONS
EFR BIT-3
0
0
1
0
1
X
X
X
1
0
1
0
EFR BIT-2
0
0
0
1
1
X
X
X
0
1
1
0
EFR BIT-1
0
X
X
X
X
0
1
0
1
1
1
1
EFR BIT-0
TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL
0
No TX and RX flow control (default and reset)
X
No transmit flow control
X
Transmit Xon1/Xoff1
X
Transmit Xon2/Xoff2
X
Transmit Xon1 and Xon2/Xoff1 and Xoff2
0
No receive flow control
0
Receiver compares Xon1/Xoff1
1
Receiver compares Xon2/Xoff2
1
Transmit Xon1/ Xoff1,
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1
Transmit Xon2/Xoff2,
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1
Transmit Xon1 and Xon2/Xoff1 and Xoff2,
Receiver compares Xon1 and Xon2/Xoff1 and Xoff2
1
No transmit flow control,
Receiver compares Xon1 and Xon2/Xoff1 and Xoff2
EFR[4]: Enhanced Function Bits Enable
Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, FCR bits 4-5, MCR bits 5-7, XFR bits
0-7 and IRPW bits 0-7 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, MCR bits 5-
7, XFR bits 0-7 and IRPW bits 0-7 are saved to retain the user settings. After a reset, the IER bits 4-7, ISR
bits 4-5, FCR bits 4-5, MCR bits 5-7, XFR bits 0-7 and IRPW bits 0-7 are set to a logic 0 to be compatible
with ST16C550 mode. (default).
• Logic 1 = Enables the above-mentioned register bits to be modified by the user.
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.
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