81C17 Datasheet, PDF (5/18 Pages) SMSC Corporation – TWENTY PIN UART (TPUART)

DIP PIN NO.
1, 2, 5-7,
9,11-12
3
4
8
10
13
14
15
16
17
18
19
20
DESCRIPTION OF PIN FUNCTIONS
NAME
SYMBOL
DESCRIPTION
DATA BUS
D0-D7 An 8-bit bi-driectional DATA BUS is used to
interface the TPUART to the processor Data Bus.
CHIP SELECT
nCS A low level on this input enables the TPUART for
reading and writing to the processor. When nCS is
high, the DATA BUS is in high impedance and the
nWR and nRD will have no effect on the chip.
READ DATA
STROBE
nRD
A low pulse on this input (when nCS is low) enables
the TPUART to place the data or the status
information on the DATA BUS.
WRITE DATA
STROBE
nWR
A low pulse on this input (when nCS is low) enables
the TPUART to accept the data or control word
from the DATA BUS into the TPUART.
GROUND
GND Power Supply Return.
CLOCK
CLK External TTL Clock Input (See Table 2)
INTERRUPT
REQUEST
nINT
An interrupt request is asserted by the TPUART
when an enabled condition has occurred in the
Status Register. This is an active low, open drain
output. This pin has an internal pullup register.
REGISTER
SELECT
RS During processor to TPUART communications, this
input is used to indicate which internal register will
be selected for access by the processor. When this
input is low, data can be written to the TX Holding
Buffer or data can be read from the RX Holding
Register. When this input is high control words can
be written to the Control Register or status
information can be read from the Status Register.
RECEIVER DATA
RX This input is the receiver serial data. A high to low
transition is required to initiate data reception.
TRANSMITTER
DATA
TX This output is the transmitted serial data from the
TPUART. When a transmission is concluded, the
TX line will always return to the mark (High) state.
CONTROL PIN 1
nCP1
This control pin is an input only pin. It can be
programmed to perform the functions of CTS or
DSR/DCD.
CONTROL PIN 2
nCP2
This control pin can be programmed to be either an
input or an output. When in input mode, this pin
can perform the functions of DSR/DCD. When in
output mode, this pin can perform the functions of
DTR or RTS.
POWER SUPPLY
VCC +5V Supply Voltage
5