XR19L212 Datasheet, PDF (16/52 Pages) Exar Corporation – TWO CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER

XR19L212
TWO CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER
FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
REV. 1.0.0
16X Clock
64 bytes by 11-bit
wide FIFO
Receive Data
Byte and Errors
Receive Data Shift Data Bit
Register (RSR)
Validation
Receive Data Characters
Receive
Data FIFO
Receive
Data
Example:
- RX FIFO trigger level selected at 16 bytes
(See Note below)
Data falls to 8 ^{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 10 (Table 14).
2.13 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 feature
is enabled to fit specific application requirement (see Figure 11):
• 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.
2.14 Auto RTS Hysteresis
The L212 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 de-
asserted until the receive FIFO reaches the upper limit of the hysteresis level. The RTS pin will be re-asserted
after the RX FIFO is unloaded to the lower limit of the hysteresis level. Under the above described conditions,
the L212 will continue to accept data until the receive FIFO gets full. The Auto RTS function is initiated when
the RTS output pin is asserted. Table 13 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 the corresponding table.
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