1 / 21

EET 405 - Advanced Digital

EET 405 - Advanced Digital. Parallel Ports. Parallel Ports. In contrast to serial ports, parallel ports ‘present’ all bits at one time. ‘The parallel port reflects a hardware engineer’s concept of the way in which communication should work.’ Eight Data bits are represented by 8 wires

lee-brennan
Télécharger la présentation

EET 405 - Advanced Digital

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EET 405 - Advanced Digital Parallel Ports

  2. Parallel Ports • In contrast to serial ports, parallel ports ‘present’ all bits at one time. • ‘The parallel port reflects a hardware engineer’s concept of the way in which communication should work.’ • Eight Data bits are represented by 8 wires • Voltage levels are standard TTL - 0/5v

  3. Parallel Ports • Flow control is provided by hardware signals • Handshaking lines • Original Parallel Ports were single direction (output only) • Modern ports allow for bi-directional communications

  4. Parallel Ports • Three ranges of I/O ports are assigned. • 03BCh, 0378h, 0278h. • LPT1, LPT2, LPT3 • Interrupts provided • 07h and 05h

  5. On 25 pin connector - IEEE 1284 1 - strobe 2-9 - data bits 0-7 10 - Acknowledge 11 - Busy 12 - Paper Out 13 - Select 14 - Auto LF 15 - error 16 - Printer Initialize 17 - Select inpu 18-25 Ground Centronics Connectors (25pin)

  6. Parallel Port Signals • Data lines - maintain the bit through the transfer period • Strobe Line • negative pulse - print character • 1 microsecond long • Busy • high = Printer is busy

  7. Acknowledge Line • normally high - strobes low to signal that printer is ready • Select • high = printer is on line • Paper Empty • high = printer is out of paper

  8. Fault (error) • high = printer has some problem not identified above • Initialize Printer • low makes printer reset itself • Select Input • low = printer should select itself

  9. Autofeed • low = automatically send LF after DR

  10. Bi-directional Parallel Ports • Dependent on the configuration of the PPI chip used • can accept 8 bit data on lines • Bus Mastering was added to allow DMA transfer to/from devices connected to parallel ports.

  11. Enhanced Parallel Ports • EPP - a faster port that has a streamlined logical interface and explicit definition of electrical parameters • Standard PP uses three input/output ports for control and moving data -- EPP uses 8 • base + 3 = EPP address port • Signals that the data bits now contain an address

  12. EPP • base + 4 to base +7 = EPP Data buffer • allows host computer to write 32 bit double word to all 4 buffers simultaneously • the 25 pin connector is assigned as a standard parallel port • When Enhanced mode is enabled - only 8 data and 5 signals are used.

  13. EPP signals • Write - pin 1 (low = write is occuring) • Data Strobe - pin 14 (data valid) • Address Strobe - pn 17 (address info is available) • Wait - pin 11 (busy) • Interrupt - pin 10 (high = request interrupt) • the other four ports are used as normal

  14. EPP CABLE • due to the high speed nature of the port, the cable is specifically engineered to reduce noise. • Double-shielded • ~ 2 Mbytes per second • can expect to increase to 8 Mbytes /sec.

  15. Extended Capabilities Ports ECP • adds 2 modes • fast two-way communication mode • data compression (RLE) • Allows for 128 addresses • Additional control registers at 0400h higher than the base registers • 0402h - Extended control register - sets mode

  16. Modes of ECP Table 19-12

  17. backwards compatible • in ECP mode - can write 8, 16, or 32 bits wide. • Allows up to 128 devices on a single port

  18. Speeds • conventional port up to 250,000 bytes per second • with overhead expect 80-90kbps • EPP can produce approx. 800 kbps • can expect up to 8 mbps in the future • ECP incorporates compression • Run Length Encoding • sends byte + multiplier

  19. Assignment

More Related