Rainbow Electronics AT75C310 - Manual (Page 60)

AT75C310
60
Modem Control and Status Signals
NCTS: Clear to Send
When low, this indicates that the modem or data set is
ready to exchange data. The NCTS signal is a modem sta-
tus input, conditions of which can be tested by the CPU
reading bit 4 (CTS) of the Modem Status Register. Bit 4 is
the complement of the NCTS signal. Bit 0 (DCTS) of the
Modem Status Register indicates whether the NCTS input
has changed state since the previous reading of the
Modem Status Register. NCTS has no effect on the trans-
mitter.
In FCM mode when the NCTS signal becomes inactive
high, the transmission of the current character will be com-
pleted and transmission stops.
Note: Whenever the CTS bit of the Modem Status Register
changes state, an interrupt is generated if the Modem
Status interrupt is enabled.
NDCD: Data Carrier Detect
When low, this indicates that the data carrier has been
detected by the modem or data set. The NDCD signal is a
modem status input, the condition of which can be tested
by the CPU reading bit 7 (DCD) of the Modem Status Reg-
ister. Bit 7 is the complement of the NDCD signal. Bit 3
(DDCD) of the Modem Status Register indicates whether
the NDCD input pin has changed since the previous read of
the Modem Status Register. NDCD has no effect on the
receiver.
Note: Whenever the DCD bit of the Modem Status Register
changes state, an interrupt is generated if the Modem
Status interrupt is enabled.
NDSR: Data Set Ready
When low, this informs the modem or data set the UART is
ready to communicate. The NDSR signal is a modem sta-
tus input, the condition of which can be tested by the CPU
reading bit 5 (DSR) of the Modem Status Register. Bit 5 is
the complement of the NDSR signal. Bit 1 (DDSR_ of the
Modem Status Register indicates whether the NDSR input
has changed state since the previous read of the Modem
Status Register.
Note: Whenever the DSSR bit of the Modem Status Register
changes state, an interrupt is generated if the Modem
Status Interrupt is enabled.
NDTR: Data Terminal Ready
When low, this informs the modem or data set that the
UART is ready to communicate. The NDTR output signal
can be set to active low by programming bit 0 (DTR) of the
Modem Control Register to a high level. A Master Reset
operation sets this signal to its inactive (high) state. Loop
mode operation holds this signal in inactive state.
NRI: Ring Indicator
When low, this indicates that a telephone ringing signal has
been received by the modem or data set. The NRI signal is
a modem status input, the condition of which can be tested
by the CPU reading bit 6 (RI) of the Modem Status Regis-
ter. Bit 6 is the complement of the NRI signal. Bit 2 (TERI)
of the Modem Status Register indicates whether the NRI
input signal has changed from a low to a high state since
the previous reading of the Modem Status Register.
Note: Whenever the RI bit of the Modem Status Register
changes from a high to a low state, an interrupt is gener-
ated if the Modem Status interrupt is enabled.
NRTS: Request to Send
When low, this informs the modem or data set that the
UART is ready to exchange data. The NRTS output signal
can be set to active low by programming bit 1 (RTS) of the
Modem Control Register. A Master Reset operation sets
this signal to its inactive (high) state. In FCM mode when
the last stop bit of a character is transmitted and the Trans-
mit Holding Register is empty, then the hardware sets
NRTS inactive high.
Note: Modem ctrl pins must be left high when not used.