XR17D154
xr
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
REV. 1.2.0
TABLE 18: 16 SELECTABLE HYSTERESIS LEVELS WHEN TRIGGER TABLE-D IS SELECTED
RTS/DTR HYSTERESIS
FCTR BIT-3 FCTR BIT-2 FCTR BIT-1 FCTR BIT-0
(CHARACTERS)
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
4
6
8
8
16
24
32
12
20
28
36
40
44
48
52
5.8.14 Enhanced Feature Register (EFR) - Read/Write
Enhanced features are enabled or disabled using this register. Bits 0-3 provide single or dual consecutive
character software flow control selection (see Table 19). When the Xon1 and Xon2 and Xoff1 and Xoff2 modes
are selected, the double 8-bit words are concatenated into two sequential characters. Caution: note that
whenever changing the TX or RX flow control bits, always reset all bits back to logic 0 (disable) before
programming a new setting.
EFR[3:0]: Software Flow Control Select
Combinations of software flow control can be selected by programming these bits. See Table 19 for complete
selections. The XOFF1/XOFF2 characters are transmitted approximately 2 character times after the RX FIFO
level has reached the RX trigger level, irrespective of which trigger table is used (Trigger Tables A-D). The
XON1/XON2 characters are transmitted when the RX FIFO level falls below the next lower trigger level for
Trigger Tables A-C and they are transmitted when the RX FIFO level falls below the (RX trigger level -
hysteresis level) for Trigger Table D. For example, if Trigger Table D is used with an RX trigger level of 56 and
a hysteresis level of 16, the XON1/XON2 characters are sent when the RX FIFO level count falls below 40.
48
EXAR [ EXAR CORPORATION ]
