PC87311AVF datasheet(60/78 Pages) NSC

60 / 78 page

70 Parallel Port (Continued)

72 DATA REGISTER (DTR)

TLF11362 – 41

This is a bidirectional data port that transfers 8-bit data The

direction is determined by the state of PDIR pin PTR7 bit

and CTR5 bit When PTR7 is low the PDIR pin will be

sensed during reset and it will determine the port direction

When PTR7 is high the CTR5 bit will determine the port

direction in conjunction with the Read and Write strobes

See PTR7 bit CTR5 POE and DPIR pins for further infor-

mation

73 STATUS REGISTER (STR)

TLF11362 – 42

This register provides status for the signals listed below It is

a read only register Writing to it is an invalid operation that

has no effect

Bits 0 1

Reserved these bits are always 1

Bit 2

In the Compatible mode this bit is always one In

the Extended mode (PTR7 bit is 1) this bit is the

IRQ STATUS bit In Extended mode if CTR4 e 1

then this bit is latched low when the ACK signal

makes a transition from 0 to 1 Reading this bit

sets it to a one This bit is the inverse of the appro-

priate IRQ signal pin

Bit 3

This bit represents the current state of the printer

error signal (ERROR) The printer sets this bit low

when there is a printer error This bit follows the

state of the ERR pin

Bit 4

This bit represents the current state of the printer

select signal (SLCT) The printer sets this bit high

when it is selected This bit follows the state of the

SLCT pin

Bit 5

This bit represents the current state of the printer

paper end signal (PE) The printer sets this bit high

when it detects the end of the paper This bit fol-

lows the state of the PE pin

Bit 6

This bit represents the current state of the printer

acknowledge signal (ACK) The printer pulses this

signal low after it has received a character and is

ready to receive another one This bit follows the

state of the ACK pin

Bit 7

This bit (BUSY) represents the current state of the

printer busy signal The printer sets this bit low

when it is busy and cannot accept another charac-

ter This bit is the inverse of the (BUSY) pin

74 CONTROL REGISTER (CTR)

TLF11362 – 43

This register provides all output signals to control the print-

er It is a read and write register except for bit 5 which is

a write-only bit

Bit 0

This bit (STB) directly controls the data strobe sig-

nal to the printer via the STB pin This bit is the

inverse of the STB pin

Bit 1

This bit (AFD) directly controls the automatic feed

XT signal to the printer via the AFD pin Setting this

bit high causes the printer to automatically feed

after each line is printed This bit is the inverse of

the AFD pin

Bit 2

This bit (INIT) directly controls the signal to initial-

ize the printer via the INIT pin Setting this bit to

low initializes the printer This bit follows the INIT

Bit 3

This bit (SLIN) directly controls the select in signal

to the printer via the SLIN pin Setting this bit high

selects the printer This bit is the inverse of the

SLIN pin

Bit 4

This bit enables the parallel port interrupt Setting

this bit low puts the appropriate IRQ5 or 7 into

TRI-STATE In the AT Compatible mode when this

bit is set high the appropriate IRQ signal follows

the ACK signal level transitions In the Extended

mode when this bit is set low the IRQ signal goes

TRI-STATE and CLEARS any pending interrupts

Setting it high the appropriate IRQ signal follows

the ACK signal and latches high on a 0 to 1 ACK’s

edge transition

Bit 5

This bit determines the parallel port direction when

Extended mode is selected (PTR7 e 1) The de-

fault condition results in the parallel port being in

the output direction (CTR5 e 0) In Compatible

mode (PTR7 e 0) this bit is reversed and reads 1

This is a WRITE ONLY bit See Table 7-2 for fur-

ther details

Bits 6 7

Reserved These bits are always 1

TABLE 7-4 Parallel Port Reset States

Signal

Control Reset

State after Reset

SLIN

TRI-STATE

INIT

ZERO

AFD

TRI-STATE

STB

TRI-STATE

IRQ5 7

TRI-STATE

PC87311AVF Datasheet(PDF) 60 Page - National Semiconductor (TI)

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