Parallel port card for PC. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Parallel port card for PC. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Computers

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The schematic diagram of the parallel port card is shown in fig. one.

(click to enlarge)

Chip DD1 - ISA data bus buffer, DD2 - output data register, DD3 - port for receiving data, set to socket XS1. On the chips DD4, DD7 and the element DD9.3, a parallel port address selector is made. The firmware of the DD7 chip is simple, since only two cells are required to burn: write 0F3h at address 0F1h (i.e., a bit at output Q0), and at address 0F2h - 0F2h (bit at output Q1). The rest of the cells contain zeros.

Chip DD5 is a port for receiving printer status signals, and DD6 is a control register. It should be noted that in a standard LPT (Standard Parallel Port - SPP) card, the Q5 output (pin 7) of the DD6 register is not used, although in most cases data is supplied to its D5 input (pin 6), and the EO input (pin 1) of the DD2 chip connected to a common wire. In LPT cards for PS/2 series machines, shown in fig. 1 connection between the output Q5 DD6 and the input EO DD2 is available, which turns the card into a bidirectional port (Simple Bidirectional Port or PS / 2 Port). In this case, the log entry. 1 to bit D5 of the control register translates DD2 into the third state, allowing an external device to set data to the inputs of DD3. After a system reset, all DD6 outputs are zero and the card is operating in standard mode.

"Pull-up" resistors R1 - R11 and load capacitors C11 - C19 correspond to the standard mode of operation of the LPT (SPP). For cards that support new speed modes (EPP, ECP), the ratings will be different, as well as the connecting cables.

Chip K556RT11 (DD7) is replaceable by K556RT4 (K556RT4A), but in this case it is necessary to introduce "pull-up" resistors with a resistance of 300 ... 510 Ohm. In the absence of a PROM, you can use a node made according to the scheme shown in Fig. 2.

Parallel Port Card for PC

The state of the address line A2 of the ISA bus is not analyzed by the selector in both cases in the same way as it is done in many LPT cards manufactured in Southeast Asia. Keep in mind that IBM has allocated addresses from 0100h to 03FFh to connect external devices to the motherboard, and only on boards of recent development is it possible to connect up to 64 K devices. If you need a full address selector, you can see its scheme in [1], which also describes the signals that determine the choice of an additional device.

Unlike the typical circuit, the output inverters of the control register are implemented on the elements of the K155LNZ (DD8) microcircuit, capable of switching current up to 40 mA and voltage up to 30 V (of course, not simultaneously). If you do not intend to connect peripherals with such parameters, you can use K555LN2 (KR1533LN2).

Another difference of the proposed card is that instead of the commonly used buffer elements K555LN1 at the input of the status register, in this case Schmitt triggers K555TL2 are used, which increases noise immunity when connecting long lines. When repeating, you need to pay attention to connecting the signal from the ACK printer (line 26) directly to input 5 of the DD10.2 (in some Chinese-made cards this connection goes through the DD9.4 inverter), although this is not so significant, since the interrupt signal from the printer is most programs are not used.

All parts of the device are placed on a standard breadboard for the ISA bus or on a homemade one, the dimensions of which, together with the XP1 printed plug, are given in [1]. The author used a prototyping board with a printed plug of the CAMAC standard, however, somewhat longer (the excess was cut off with a hacksaw). The XS1 socket is a standard DRB-25F, soldered from a faulty multi-card, the double-row PLD pin connectors with an MJ-0 jumper as S1, S2 and capacitors similar to domestic oxide K50-35 and ceramic KD-2 are taken from there. Instead of K555IR23 (DD2), it is convenient to use KR1533IR37 with inputs and outputs located on opposite sides of the case.

To check the assembled device, you can use the verification programs described in [2]. Some of them require loopback plugs to be installed on the XS1 output socket. The connections of the mating part of the connector (DB-25M plug) for the NDiags programs from the Norton Utilities and Checkit kits are shown in fig. 3, a and b.

Parallel Port Card for PC

Checking the operation of the card in bidirectional mode was carried out using the program parallel.exe by Parallel Software. It is also possible to check the card with the help of self-made programs, bearing in mind that the address of the LPT1 card data register is 378H (278H), the control register is 37AH (27AH), the status register (read only) is 379H (279H). The addresses in brackets are for LPT2. The distribution of signals by bits for the control register (Control Register) is indicated in Table. 1, for the status register (Status Register) - in table. 2. Bits not listed in the tables are not used and must be masked in software.

Parallel Port Card for PC

In conclusion, it should be noted that the described card expands the capabilities of a standard parallel port, but does not add ECP and EPP modes that require additional registers. The possibilities provided by these modes and their programming can be found in [3].

Literature

Ryumik S. Secrets of the IBM PC Game Port. - Radio, 2000, No. 1, p. 27-29, 35.
Trushin N. Utilities for IBM-compatible computers. - Radio, 2000, No. 10, p. 26, 27.
Dolgy A. Programmer of Flash-memory chips. - Radio, 2000, No. 10, p. 23-25.

Author: V. Mikheev, Moscow

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