XR16C864 Datasheet, PDF (16/51 Pages) Exar Corporation – 2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO

XR16C864
2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO
FIGURE 9. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
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REV. 2.0.1
16X Clock
128 bytes by 11-bit
wide
FIFO
Receive Data
Byte and Errors
Receive Data Shift
Register (RSR)
Receive
Data FIFO
Receive
Data
Data Bit
Validation
Receive Data Characters
E xam p le
- :RX FIFO trigger level selected at 16
bytes
Data falls to
8
(See Note Below)
RTS# re-asserts when data falls below the flow
control trigger level to restart remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
FIFO
Trigger=16
RHR Interrupt (ISR bit-2) programmed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
Data fills to
24
RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
RXFIFO1
NOTE: Table-B selected as Trigger Table for Figure 9 (Table 11).
2.14 Auto RTS Hardware Flow Control
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see Figure 10):
• Enable auto RTS flow control using EFR bit-6.
• The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).
If using the Auto RTS interrupt:
• Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1.
2.15 Auto RTS Hysteresis
The 864 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with the
XR16C850, ST16C650A and ST16C550 family of UARTs. With the Auto RTS function enabled, an interrupt is
generated when the receive FIFO reaches the programmed RX trigger level. The RTS# pin will not be forced
to a logic 1 (RTS off), until the receive FIFO reaches the upper limit of the hysteresis level. The RTS# pin will
return to a logic 0 after the RX FIFO is unloaded to the lower limit of the hysteresis level. Under the above
described conditions, the 864 will continue to accept data until the receive FIFO gets full. The Auto RTS
function is initiated when the RTS# output pin is asserted to a logic 0 (RTS On). Table 15 shows the complete
details for the Auto RTS# Hysteresis levels. Please note that this table is for programmable trigger levels only
(Table D). The hysteresis values for Tables A-C are the next higher and next lower trigger levels in Tables A-C
(See Table 11).
2.16 Auto CTS Flow Control
Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is
monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific
application requirement (see Figure 10):
• Enable auto CTS flow control using EFR bit-7.
If using the Auto CTS interrupt:
16