BIT 3 nERR - nERROR
The level on the nERROR input is read by the CPU as bit 3 of the Printer Status Register. A logic 0 means an error has
been detected; a logic 1 means no error has been detected.
BIT 4 SLCT - PRINTER SELECTED STATUS
The level on the SLCT input is read by the CPU as bit 4 of the Printer Status Register. A logic 1 means the printer is on
line; a logic 0 means it is not selected.
BIT 5 PE - PAPER END
The level on the PE input is read by the CPU as bit 5 of the Printer Status Register. A logic 1 indicates a paper end; a
logic 0 indicates the presence of paper.
BIT 6 nACK - nACKNOWLEDGE
The level on the nACK input is read by the CPU as bit 6 of the Printer Status Register. A logic 0 means that the printer
has received a character and can now accept another. A logic 1 means that it is still processing the last character or has
not received the data.
BIT 7 nBUSY - nBUSY
The complement of the level on the BUSY input is read by the CPU as bit 7 of the Printer Status Register. A logic 0 in
this bit means that the printer is busy and cannot accept a new character. A logic 1 means that it is ready to accept the
next character.
CONTROL PORT
ADDRESS OFFSET = 02H
The Control Port is located at an offset of '02H' from the base address. The Control Register is initialized by the RESET
input, bits 0 to 5 only being affected; bits 6 and 7 are hard wired low.
BIT 0 STROBE - STROBE
This bit is inverted and output onto the nSTROBE output.
BIT 1 AUTOFD - AUTOFEED
This bit is inverted and output onto the nAUTOFD output. A logic 1 causes the printer to generate a line feed after each
line is printed. A logic 0 means no autofeed.
BIT 2 nINIT - nINITIATE OUTPUT
This bit is output onto the nINIT output without inversion.
BIT 3 SLCTIN - PRINTER SELECT INPUT
This bit is inverted and output onto the nSLCTIN output. A logic 1 on this bit selects the printer; a logic 0 means the
printer is not selected.
BIT 4 IRQE - INTERRUPT REQUEST ENABLE
The interrupt request enable bit when set to a high level may be used to enable interrupt requests from the Parallel Port
to the CPU. An interrupt request is generated on the IRQ port by a positive going nACK input. When the IRQE bit is
programmed low the IRQ is disabled.
BIT 5 PCD - PARALLEL CONTROL DIRECTION
Parallel Control Direction is not valid in printer mode. In printer mode, the direction is always out regardless of the state
of this bit. In bi-directional, EPP or ECP mode, a logic 0 means that the printer port is in output mode (write); a logic 1
means that the printer port is in input mode (read).
Bits 6 and 7 during a read are a low level, and cannot be written.
EPP ADDRESS PORT
ADDRESS OFFSET = 03H
The EPP Address Port is located at an offset of '03H' from the base address. The address register is cleared at
initialization by RESET. During a WRITE operation, the contents of the internal data bus DB0-DB7 are buffered (non
inverting) and output onto the PD0 - PD7 ports. An LPC I/O write cycle causes an EPP ADDRESS WRITE cycle to be
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