Slow AMBA Peripherals
13-17
GMS30C7201 Data Sheet
Interrupt Enable Register
This register enables the five types of UART interrupts. Each interrupt can individually
activate the interrupt (INTUART) output signal. It is possible to totally disable the
interrupt Enable Register (IER). Similarly, setting bits of the IER register to a logic 1,
enables the selected interrupt(s). Disabling an interrupt prevents it from being indicated
as active in the IIR and from activating the INTUART output signal. All other system
functions operate in their normal manner, including the setting of the Line Status and
MODEM Status Registers.
Table 13-6: Summary of registers
on page 13-10 shows
the contents of the IER. Details on each bit follow.
Bit 0:
This bit enables the Received Data Available Interrupt (and time-out
interrupts in the FIFO mode) when set to logic 1.
Bit 1:
This bit enables the Transmitter Holding Register Empty Interrupt
when set to logic 1.
Bit 2:
This bit enables the Receiver Line Status Interrupt when set to logic 1.
Bit 3:
This bit enables the MODEM Status Interrupt when set to logic 1.
Bit 4
–
7:
These four bits are always logic 0.
MODEM Control Register
This register controls the interface with the MODEM or data set (or a peripheral device
emulating a MODEM). The contents of the MODEM Control Register are indicated in
Table 13-6: Summary of registers
on page 13-10 and are described below.
Bit 0:
This bit controls the Data Terminal Ready (
NDTR
) output. When bit is
set to a logic 1, the
NDTR
output is forced to a logic 0. When bit 0 is
reset to a logic 0, the
NDTR
output is forced to a logic 1.
Note: The
NDTR
output of the UART may be applied to an EIA
inverting line driver (such as the DS1488) to obtain the proper polarity
input at the succeeding MODEM or data set.
Bit 1:
This bit controls the Request to Send (
NRTS
) output. Bit 1 affects the
NRTS
output in a manner identical to that described above for bit 0.
Bit 2:
Not used
Bit 3:
Not used
Bit 4:
This bit provides a local loopback feature for diagnostic testing of the
UART. When bit 4 is set to logic 1, the following occur: the transmitter
Serial Output (
SOUT
) is set to the Marking (logic 1) state; the receiver
Serial Input (
SIN
) is disconnected; the output of the Transmitter Shift
Register is
“
looped back
”
into the Receiver Shift Register input; the
four MODEM Control inputs (
NCTS
,
NDSR
,
NDCD
and
NRI
) are
disconnected; and the two MODEM Control outputs (NDTR and
NRTS) are internally connected to the four MODEM Control inputs,
and the MODEM Control output pins are forced to their inactive state
(HIGH). On the diagnostic mode, data that is transmitted is
immediately received. This feature allows the processor to verify the
transmit- and received-data paths of the UART.
In the diagnostic mode, the receiver and transmitter interrupts are fully
operational. Their sources are external to the part. The MODEM
Control interrupts are also operational, but the interrupts sources are
now the lower four bits of the MODEM Control Register instead of the
four MODEM Control inputs. The interrupts are still controlled by the
Interrupt Enable Register.
Bit 5
–
7:
These bits are permanently set to logic 0.