
SMSC DS – FDC37N958FR
Page 104
Rev. 09/01/99
STATUS PORT
ADDRESS OFFSET = 01H
The Status Port is located at an offset of '01H'
from the base address. The contents of this
register are latched for the duration of an nIOR
read cycle. The bits of the Status Port are defined
as follows:
BIT 0 TMOUT - TIME OUT
This bit is valid in EPP mode only and indicates
that a 10 usec time out has occured on the EPP
bus. A logic “0” means that no time out error has
occured; a logic “1” means that a time out error
has been detected. This bit is cleared by a
RESET. Writing a one to this bit clears the time
out status bit. On a write, this bit is self clearing
and does not require a write of a “0”. Writing a “0”
to this bit has no effect.
BITS 1, 2
- are not implemented as register bits,
during a read of the Printer Status Register these
bits are a low level.
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.