
=
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36
Versi on 0. 4, March/2000
signal
both
- GPIO[0:7]/
ED[0:7]
(in/out) :
0 is the
Operation Modes :
(Left for Blank)
the peripheral may drive this pin low to request communications with the host. This
would be typically used to generate an interrupt to the host. This signal is valid in
forward and reverse trnasfers.
8-bit bus used to hold data, address or command information in all modes. The bit
most significant bit.
5.10 UART
Overview :
The W90221 contains two Universal Asynchronous Receiver/Transmitter (UART) ports, one of them
provides complete MODEM-control and serial transfermation capabilities, whereas the other one provides
only serial transfermation capability. The UART performs serial-to-parallel conversion on data characters
received from a peripheral device such as MODEM, and parallel-to-serial conversion on data characters
received from the CPU. One 16 bytes transmitter FIFO (TX-FIFO) and one 16 bytes (plus 3 bits of error
data per byte) receiver FIFO (RX-FIFO) have been built in to reduce the number of interrupts presented to
the CPU. The CPU can read the complete status of the UART at any time during the functional operation.
Status reported includes error conditions (parity, overrun, framing, or break interrupt) and states of TX-FIFO
and RX-FIFO.
Block Diagram :
Features :
transmitter and receiver are each buffered with 16 bytes FIFO's to reduce the number of interrupts
presented to the CPU
MODEM control functions (CTS, RTS, DSR, DTR, RI and DCD)
Fully programmable serial-interface characteristics :
TX-FIFO (16x8)
& Control
Baud Rate
Generator
32-bit CPU bus
TX shift register
RX-FIFO (16x8)
& Control
RX shift register
SDI
SDO
8
8
Fig 5.1.5-1 UART Block Diagram
OSC (14.318Mhz)
RTS#
DTR#
OUT1#
OUT2#
CTS#
DSR#
DCD#
RI#
Modem
Control
Reg
Modem
Status
Reg
8