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./ˈzɛbrə/ZEB-rə/ˈziːbrə/ZEE-brə[1]

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

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

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

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

FPGA Device Utilisation FPGA is almost full...

Logic block layout

How do you configure ZEBRA? 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

The System Bus

AND/OR Blocks INP1 INP2 AND1

GATE Blocks INP1 INP2 GATE1

DIV Blocks INP1 COUNT OUTD

PULSE Blocks INP1 PULSE1 PULSE2

QUAD Blocks STEP OUTA OUTB

PC Setup

PC Plot

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...

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