ST16C552AIJ68 datasheet(24/39 Pages) EXAR

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ST16C552/552A

Rev. 3.40

MSR BIT-6:

RI (active high, logical 1). Normally this bit is the

compliment of the -RI input. In the loop-back mode

this bit is equivalent to MCR bit-2 in the MCR register.

MSR BIT-7:

CD (active high, logical 1). Normally this bit is the

compliment of the -CD input. In the loop-back mode

this bit is equivalent to MCR bit-3 in the MCR register.

Note: Whenever any MSR bit 0-3: is set to logic “1”, a

MODEM Status Interrupt will be generated.

Scratchpad Register (SPR)

The ST16C552/552A provides a temporary data reg-

ister to store 8 bits of user information.

PRINTER PORT REGISTER DESCRIPTIONS

Port Register (PR)

PR BIT 0-7:

Printer Data port (Bi-directional) - These pins are the

eight bit data bus for transferring information to or

from an external device (usually a printer). D0 is the

least significant bit. PD7-PD0 are latched during a

write cycle (output mode).

I/O Select Register (IOSEL)

This bit is used in conjunction with the state of BIDEN

to set the direction (input/output) of the PD7-PD0 data

bus. This register is used only when BIDEN is a logic

Logic 55 (Hex) + BIDEN 0 = PD7-PD0 are set for

output mode

Logic AA (Hex) + BIDEN 0 = PD7-PD0 are set for input

mode

Status Register (SR)

This register provides the printer port input logical

states and the status of the interrupt -INTP based on

the condition of the -ACK printer port interface signal.

The logical state of these pins is dependent on exter-

nal interface signals.

SR BIT 1-0:

Not Used - initialized to a logic 1.

SR BIT-2:

Logic 0 = an interrupt is pending

When INTSEL is a logic 0, SR bit-2 basically tracks the

-ACK input interface pin (returns to a logic 1 when the

-ACK input returns to a logic 1). However when

INTSEL is a logic 1, the latched mode is selected, SR

bit-2 goes to a logic 0 with the -ACK input but does not

return to a logic 1 until the end of the read cycle, i.e.,

reading SR will set this bit to a logic 1.

Logic 1 = no interrupt is pending. (normal inactive

state)

SR BIT-3:

Logic 0 = -ERROR input is a logic 0.

Logic 1 = -ERROR input is a logic 1. (normal inactive

state)

SR BIT-4:

Logic 0 = SLCT input is a logic 0. (normal inactive

state)

Logic 1 = SLCT input is a logic 1.

SR BIT-5:

Logic 0 = PE input is a logic 0. (normal inactive state)

Logic 1 = PE input is a logic 1.

SR BIT-6:

Logic 0 = -ACK input is a logic 0.

Logic 1 = -ACK input is a logic 1. (normal inactive

state)

SR BIT-7:

Logic 0 = BUSY input is a logic 0

Logic 1 = BUSY input is a logic 1 (normal inactive

state)

Command Register (COM)

This register provides the printer port input logical

states and the status of the printer interrupt INIT,

which is based on the state of CON bit-1.

COM BIT-0:

-STROBE is a bi-directional signal with an open

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