Slow AMBA Peripherals
13-4
GMS30C7201 Data Sheet
13.2.3 Signal description
The 16C550 UART module is connected to the internal APB bus.
Name
Type
Source/
Destination
Description
PCLK
In
UART Clock input
This connects the main timing reference to the UART.
3.6864Mhz is input clock frequency recommended.
BnRES
In
APB Bridge
Reset signal generated from the APB Bridge (Master Reset)
When this input is LOW, it clears all the registers (except the
Receiver Buffer, Transmitter Holding and Divisor Latches)
and the control logic of the UART. The states of various
output signals (
SOUT
,
INTUART
,
NRTS
,
NDTR
) are
affected by an active BnRES input.
PA[5:2]
In
APB Bridge
Register select. Address signals connected to these three
inputs select a UART register for the CPU to read from or
write to during data transfer. A table of registers and their
addresses is shown below (
Table 13-6: Summary of
registers
on page 13-10).
PD[7:0]
InOut
APB Bridge
Data Bus. This bus comprises eight TRI-STATE input/output
lines. The bus provides bi-directional communications
between the UART and the CPU, Data, control words and
status information are transferred via the PD[7:0] data bus.
PSTB
In
APB Bridge
This strobe signal is used to time all accesses on the
peripheral bus. The falling edge of
PSTB
is coincident with
the falling edge of
BCLK
(ASB System Clock).
PWRITE
In
APB Bridge
When HIGH, this signal indicates a write to a peripheral.
When LOW, it indicates a read from a peripheral.
This signal has the same timing as the peripheral address
bus. It becomes valid before
PSTB
goes HIGH and remains
valid after
PSTB
goes LOW.
PSEL
In
APB Bridge
When HIGH, this signal indicates that this module has been
selected by the APB bridge. This selection is a decode of the
system address bus (ASB).
INTUART
Out
INTC
Interrupt. This pin goes HIGH whenever any one of the
following interrupt types has an active HIGH condition and is
enabled via IER:
Receiver Error Flag
Received Data Available:timeout(FIFO Mode only)
Transmitter Holding Register Empty
MODEM Status
The INTUART signal is reset LOW upon the appropriate
interrupt service or a Master Reset operation.
SIN
In
External
Serial Input. Serial data input from the communications link
(peripheral device, MODEM or data set).
Table 13-2: Signal descriptions