eee410_lecture18 - EEE 410 Microprocessors I Spring 04/05...

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1 EEE 410 – Microprocessors I Spring 04/05 – Lecture Notes # 18 Outline of the Lecture Interfacing the Parallel Port Standard Parallel Port (SPP) Port addresses Software registers and programming Bi-directional ports Using parallel port’s IRQ Enhanced Parallel Port (EPP) Extended Capabilities Port (ECP) Standard Parallel Port ¾ The Parallel Port is the most commonly used port for interfacing. This port will allow the input of up to 9 bits or the output of 12 bits at any one given time, thus requiring minimal external circuitry to implement many simpler tasks. ¾ It's found commonly on the back of your PC as a D-Type 25 Pin female connector . Parallel Port’s are standardized under the IEEE 1284 standard first released in 1994. This standard defines 5 modes of operation which are as follows, ¾ 1. Compatibility Mode. (Centronics Mode) 2. Nibble Mode. 3. Byte Mode. 4. EPP Mode (Enhanced Parallel Port). 5. ECP Mode (Extended Capabilities Mode). ¾ Compatibility mode is also known as " Centronics Mode ". In this mode you can only output data. ¾ To receive/ input data, you must change the mode to either Nibble or Byte mode. Nibble mode can input a nibble (4 bits) from device to computer . ¾ Byte mode uses the Parallel's bi-directional feature (found only on some cards) to input a byte (8 bits) of data. ¾ Extended and Enhanced Parallel Ports use additional hardware to generate and manage handshaking . ¾ For example, to output a byte to a printer (or anything in that matter) using compatibility mode, the software must, 1. Write the byte to the Data Port . 2. Check to see is the printer is busy. If the printer is busy, it will not accept any data, thus any data which is written will be lost. 3. Take the Strobe (Pin 1) low. This tells the printer that there is the correct data on the data lines/pins (Pins 2-9). 4. Put the strobe high again after waiting approximately 5 microseconds after putting the strobe low. (Step 3) ¾ This limits the speed at which the port can run at. The EPP & ECP ports get around this by letting the hardware check to see if the printer is busy and generate a strobe and /or appropriate handshaking. This means only one I/O instruction need to be performed, thus increasing the speed. These ports can output at around 1-2
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2 megabytes per second . The ECP port also has the advantage of using DMA channels and FIFO buffers, thus data can be shifted around without using I/O instructions. Port Addresses The Parallel Port has three commonly used base addresses. LPT1 is normally assigned base address 378h , while LPT2 is assigned 278h. 378h & 278h have always been commonly used for Parallel Ports. Address Notes: 3BCH - 3BFH Used for Parallel Ports which were incorporated on to Video Cards - Doesn't support ECP addresses 378H - 37FH Usual Address For LPT 1 278H - 27FH Usual Address For LPT 2 Table 2 Port Addresses Hardware Properties ¾ Below is a table of the "Pin Outs" of the D-Type 25 Pin connector and the Centronics 34 Pin connector. The D-Type 25 pin connector is the most common connector found
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eee410_lecture18 - EEE 410 Microprocessors I Spring 04/05...

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