Intel CONTROLLERS 413808 - Manual (Page 661)

Intel ® 413808 and 413812 I/O Controllers in TPER Mode
October 2007 Developer’s Manual
Order Number: 317805-001US 661
UARTs—Intel ® 413808 and 413812
13.2 Signal Descriptions
The name and description of external signals connected to a UART module are shown in
Table 442 .
Note: * “x” in signal name replaced with either “0” or “1” for UART-0 or UART-1 respectively.
Table 442. UART Signal Descriptions
Name* Type Description
Ux_RXD Input SERIAL INPUT: Serial data input from device pin to the receive shift register.
Ux_TXD Output
SERIAL OUTPUT: Composite serial data output to the communications link-peripheral, modem, or
data set. The TXD signal is set to the MARKING (logic 1) state upon a Reset operation.
Ux_CTS# Input
CLEAR TO SEND: When low, this pin indicates that the receiving UART is ready to receive data.
When the receiving UART deasserts CTS# high, the transmitting UART should stop transmission to
prevent overflow of the receiving UARTs buffer. The CTS# signal is a modem-status input whose
condition can be tested by the host processor or by the UART when in Autoflow mode as described
below:
Non-Autoflow Mode: When not in Autoflow mode, bit 4 (CTS) of the Modem Status register (MSR)
indicates the state of CTS# . Bit 4 is the complement of the CTS# signal. Bit 0 (DCTS) of the Modem
Status register indicates whether the CTS# input has changed state since the previous reading of
the Modem Status register. CTS# has no effect on the transmitter. The user can program the UART
to interrupt the processor when DCTS changes state. The programmer can then stall the outgoing
data stream by starving the transmit FIFO or disabling the UART with the IER register.
Note: When UART transmission is stalled by disabling the UART, the user does not receive an MSR
interrupt when CTS# reasserts. This is because disabling the UART also disables interrupts. To get
around this, the user can use Auto CTS in Autoflow Mode, or program the CTS# pin to interrupt.
Autoflow Mode: In Autoflow mode, the UART Transmit circuity checks the state of CTS# before
transmitting each byte. When CTS# is high, no data is transmitted. See Section 13.4.7, UART x
Modem Control Register for more information on Auto CTS mode.
Ux_RTS# Output
REQUEST TO SEND: When low, this informs the remote device that the UART is ready to receive
data. A reset operation sets this signal to its Inactive (high) state. LOOP mode operation holds this
signal in its Inactive state.
Non-Autoflow Mode: The RTS# output signal can be asserted by setting bit 1 (RTS) of the Modem
Control register to a 1. The RTS bit is the complement of the RTS# signal.
Autoflow Mode: RTS# is automatically asserted by the autoflow circuitry when the Receive buffer
exceeds its programmed threshold. It is deasserted when enough bytes are removed from the buffer
to lower the data level back to the threshold. See
Section 13.4.7, UART x Modem
Control Register
for more information on Auto RTS mode.