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ZEBRA

ZEBRA. Tom Cobb. What is a zebra?. Zebras ( /ˈzɛbrə/ ZEB -rə or /ˈziːbrə/ ZEE -brə ) [1] are several species of African equids (horse family) united by their distinctive black and white stripes. What is ZEBRA?. A digital signal level converter and position capture box

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ZEBRA

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  1. ZEBRA Tom Cobb

  2. What is a zebra? • Zebras (/ˈzɛbrə/ZEB-rə or /ˈziːbrə/ZEE-brə)[1] are several species of African equids (horse family) united by their distinctive black and white stripes.

  3. What is ZEBRA? • A digital signal level converter and position capture box • 1U metal box with front panel BNCs and Lemos and rear panel encoder inputs

  4. What does ZEBRA do? • Takes front panel single channel inputs • TTL, LVDS, PECL, NIM, Open Collector • And rear panel incremental encoder signals • A+B RS422 Quadrature decoder, Z, connected • Pass the signals through some FPGA logic • Logic gates, position capture circuitry • Ouput front and rear panel signals • Same format as inputs, rewirable at run time

  5. FPGA Choice • Spartan-6 : Low risk, low cost and low power for cost-sensitive applications. • Available in TQG144 package. • Cost : ~ £10

  6. FPGA Device Utilisation • FPGA is mainly occupied by two modules. • Logic Control (41%) • Position Capture (37%) • SRAM Controller (7%) • Picoblaze Comms (3%)

  7. FPGA Device Utilisation • FPGA is almost full...

  8. Logic block layout

  9. How do you configure ZEBRA? • 115200 baud RS232 link to EPICS • Parameters set/get via EPICS • Logic blocks rewired via the system bus • Data download of position/time information • Save to internal flash

  10. The System Bus

  11. AND/OR Blocks INP1 INP2 AND1

  12. GATE Blocks INP1 INP2 GATE1

  13. DIV Blocks INP1 COUNT OUTD

  14. PULSE Blocks INP1 PULSE1 PULSE2

  15. QUAD Blocks STEP OUTA OUTB

  16. PC Setup

  17. PC Plot

  18. What doesn’t ZEBRA do? • Analogue • Signals < 20ns • Low latency data transfer • High bandwidth data transfer • Sequencing • Absolute encoders (yet) • For these we would need a ZEBRA2...

  19. Summary • ZEBRA is some level converter circuitry and an FPGA to do logic and position capture • EPICS interface over serial line • Parts cost about £500 each • Looking at making them available for other sites if there is interest

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