XR16C854 Datasheet, PDF (33/51 Pages) Exar Corporation – QUAD UART WITH RX/TX FIFO COUNTERS,128-BYTE FIFO

XR16C854
Table 8, SOFTWARE FLOW CONTROL FUNCTIONS
Cont-3 Cont-2 Cont-1 Cont-0 TX, RX software flow controls
0
0
X
X
No transmit flow control
1
0
X
X
Transmit Xon1/Xoff1
0
1
X
X
Transmit Xon2/Xoff2
1
1
X
X
Transmit Xon1 and Xon2/Xoff1 and Xoff2
X
X
0
0
No receive flow control
X
X
1
0
Receiver compares Xon1/Xoff1
X
X
0
1
Receiver compares Xon2/Xoff2
1
0
1
1
Transmit Xon1/ Xoff1.
Receiver compares Xon1 and Xon2,
Xoff1 and Xoff2
0
1
1
1
Transmit Xon2/Xoff2
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
0
0
1
1
No transmit flow control
Receiver compares Xon1 and Xon2/Xoff1 and Xoff2
EFR BIT-4:
Enhanced function control bit. The content of the IER
bits 4-7, ISR bits 4-5, FCR bits 4-5, and MCR bits 5-7
can be modified and latched. After modifying any bits
in the enhanced registers, EFR bit-4 can be set to a
logic 0 to latch the new values. This feature prevents
existing software from altering or overwriting the 854
enhanced functions.
Logic 0 = 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, then IER bits 4-7, ISR
bits 4-5, FCR bits 4-5, and MCR bits 5-7 are initialized
to the default values shown in the Internal Resister
Table. 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 ST16C554 mode. (normal default
condition).
Logic 1 = Enables the enhanced functions. When this
bit is set to a logic 1 all enhanced features of the 854
are enabled and user settings stored during a reset will
be restored.
EFR BIT-5:
Logic 0 = Special Character Detect Disabled. (normal
default condition)
Logic 1 = Special Character Detect Enabled. The 854
compares each incoming receive character with Xoff-
2 data. If a match exists, the received data will be
transferred to FIFO and ISR bit-4 will be set to indicate
detection of special character. Bit-0 in the X-registers
corresponds with the LSB bit for the receive character.
When this feature is enabled, the normal software flow
control must be disabled (EFR bits 0-3 must be set to
a logic 0).
EFR BIT-6:
Automatic RTS may be used for hardware flow control
by enabling EFR bit-6. When AUTO RTS is selected,
an interrupt will be generated when the receive FIFO
is filled to the programmed trigger level and -RTS will
go to a logic 1 at the next trigger level. -RTS will return
to a logic 0 when data is unloaded below the next lower
trigger level (Programmed trigger level -1). The state
of this register bit changes with the status of the
Rev. 1.00P
33