EET 405 - Advanced Digital

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

6. 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)

7. 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

8. 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

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

10. Autofeed • low = automatically send LF after DR

11. 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.

12. 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

13. 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.

14. 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

15. 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.

16. 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

17. Modes of ECP Table 19-12

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

20. 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

21. Assignment