PC87303 datasheet(14/114 Pages) NSC

14 / 114 page

10 Pin Description (Continued)

TABLE 1-1 Pin Descriptions (Alphabetical)

(Continued)

Symbol

Function

PDWN

Power-Down

This multi-function pin stops the clocks andor the external crystal based on the

selections made in the Power and Test Register (PTR) bits 1 and 2 (See CSOUT for additional

information)

123

Paper End

This input is set high by a connected printer which is out of paper This pin has a

nominal 25 kX pull-down resistor attached to it

PWRGOOD

Power Supply Good

An input to the PC87303 indicating that the power supply is good This input

should be held low until the power supply is stable

Read

Active low input to signal a data read by the microprocessor

RDATA

Read Data

This input is the raw serial data read from the floppy disk drive

RI12

107 97

Ring Indicator

When low this indicates that a telephone ring signal has been received by the

MODEM The RI signal is a MODEM status input whose condition the CPU can test by reading bit

6 (RI) of the MODEM Status Register (MSR) for the appropriate serial channel Bit 6 is the

complement of the RI signal Bit 2 (TERI) of the MSR indicates whether the RI input has changed

from low to high since the previous reading of the MSR

Note

When the TERI bit of the MSR is set an interrupt is generated if MODEM Status interrupts are enabled

RTS12

111 103

Request to Send

When low this output indicates to the MODEM or data set that the UART is

ready to exchange data The RTS signal can be set to an active low by programming bit 1 (RTS) 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 to its inactive state (See CFG0 – 4 for

further information)

SIN12

112 104

Serial Input

This input receives composite serial data from the communications link (eg

peripheral device MODEM or data set)

SLCT

122

Select

When a printer is connected it sets this input high This pin has a nominal 25 kX pull-down

resistor attached to it

SLIN

119

Select Input

When this signal is low it selects the printer This pin is a TRI-STATE condition 10 ns

aftera0is loaded into the corresponding Control Register bit The system should pull this pin high

using a 47 kX resistor

SOUT12

110 100

Serial Output

This output sends composite serial data to the communications link (peripheral

device MODEM or data set) The SOUT signal is set to a marking state (logic 1) after a Master

Reset operation (See BOUT and CFG0 – 4 for further information)

STB

135

Data Strobe

This output indicates to the printer that valid data is available at the printer port This

pin is in a TRI-STATE condition 10 ns after a zero is loaded into the corresponding Control

information)

STEP

Step

This output signal issues pulses to the disk drive at a software programmable rate to move

the head during a seek operation

SYNC

Synch

32 kHz Real-Time Clock output signal when bit 4 of KRR is 1 SYNC is an input when MR

is high and is sampled by the falling edge of MR It is a TTL strap input buffer It is sampled to bit 2

of PTR A 40 kX internal pullup resistor is present on this pin

SYSCLK

System Clock

This input is the system clock when bit 7 of CS1CF0 is 0 (See CS1 for further

information)

Test 0

This input can be directly tested by the conditional jump instructions JT0 and JNT0 of the

Keyboard Controller

Test 1

This input can be directly tested by the conditional jump instructions JT1 and JNT1 of the

Keyboard Controller T1 can also be used as the external input to the 8-bit countertimer of the

Keyboard Controller

Terminal Count

Control signal from the DMA controller to indicate the termination of a DMA

transfer TC is accepted only when FDACK or PDACK is active TC is active high in PC-AT and

Model 30 modes and active low in PS2 mode

PC87303 Datasheet(PDF) 14 Page - National Semiconductor (TI)

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