TL16C552 Datasheet, PDF (23/33 Pages) Texas Instruments – DUAL ASYCHRONOUS COMMUNICATIONS ELEMENT WITH FIFO

TL16C552
DUAL ASYCHRONOUS COMMUNICATIONS ELEMENT
WITH FIFO
SLLS102B – DECEMBER 1990 – REVISED MARCH 1996
PRINCIPLES OF OPERATION
line printer port (LPT) (continued)
Table 6 summarizes the possible combinations of extended mode and the direction control bit. In either
case, the bits of the LPD register are defined as follows:
Table 6. Extended Mode and Direction Control Bit Combinations
PEMD
DIR
PD0 – PD7 FUNCTION
L
X
PC/AT mode – output
H
0
PS/2™ mode – output
H
1
PS/2™ mode – input
register 1 read line printer status register
The line printer status (LPS) register is a read-only register that contains interrupt and printer status of the LPT
connector terminals. In Table 7 (in the default column), are the values of each bit after reset in the case of the
printer being disconnected from the port.
Table 7. LPS Register Bit Description
BIT
DESCRIPTION
DEFAULT
0
Reserved
1
1
Reserved
1
2
PRINT
1
3
ERR
†
4
SLCT
†
5
PE
†
6
ACK
†
7
BSY
†
† _{Outputs are dependent upon device inputs.}
D Bits 0 and 1: These bits are reserved and are always set.
D Bit 2: This bit is the printer interrupt (PRINT, active low) status bit. When cleared indicates that the printer
has acknowledged the previous transfer with an ACK handshake (bit 4 of the control register is set). The
bit is cleared on the active to inactive transition of the ACK signal. This bit is set after a read of the status
port.
D Bit 3: This bit is the error (ERR, active low) status bit corresponds to ERR input.
D Bit 4: This bit is the select (SLCT) status bit corresponds to SLCT input.
D Bit 5: This bit is the paper empty (PE) status bit corresponds to PE input.
D Bit 6: This bit is the acknowledge (ACK, active low) status bit corresponds to ACK input.
D Bit 7: This bit is the busy (BSY, active low) status bit corresponds to BUSY input (active high).
register 2 line printer control (LPC) register
The LPC register is read/write port that controls the PD0 – PD7 direction and drive the printer control lines. Write
operations set or clear these bits, while read operations return the state of the last write operation to this register.
The bits in this register are described in Table 8.
PS/2 is a trademark of International Business Machines Corporation.
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