Specification of RF Monitor Module

Author: C. Brown

General Description

This CAMAC module has four basic inputs: the accelerator RF signal, a beam gate start and stop, and a reference signal. The reference signal presumably comes from a single short counter or a simple coincidence of short counters that has a good beam-on/off ratio, well-defined timing, and a 10 KHz to 1 Mhz rate. The module compares the phase of the reference signal to the RF and produces a phase-shifted output RF signal that is phase-locked to the reference signal within 15 psec on average.

The module works by shifting the RF phase by 15 psec whenever it sees the apparent time difference between the phase-shifted RF and the reference counter fall outside a preset window eight times in a row in the same direction. The width of the coincidence window is internally set to 1 nsec (but it can be increased up to 2 nsec). The module displays the phase shift in units of 15 psec. on the front panel.

The module also calculates and displays the apparent duty cycle of the reference signal. The time delay used in the self-referential duty cycle calculation can be set by CAMAC from 0 to 38.57 usec.

Internal settings of the module can be set and read via CAMAC. A CAMAC read, F0A0, yields the current value of the RF phase shift. An F0A1 read yields the value of the duty factor calculated at the end of each spill.

Detailed Description of Module

LIST OF CAMAC FUNCTIONS.
Function Description Code
Read Phase Shift F0A0
Read Duty Cycle F0A1
Read Coincidence Delay F0A2
Read Command F0A3
Read Status F0A4
Read Error F0A5
Read Module ID F6A0
Read Module Serial Number F6A1
Write Command F16A0
Write Coincidence Delay F16A1
Clear Module Registers F9A0
Clear Command Register F21A0

LIST OF CAMAC STANDARD LAM FUNCTIONS
Function Description Code
Read LAM Status F1A12
Read LAM Mask F1A13
Read LAM Request F1A14
Test LAM F8A15
Clear LAM Registers F10A15
ClearLAM Status F11A12
Clear LAM Mask F11A13
Set LAM Status F19A12
Set LAM Mask F19A13
Reset LAM Status F23A12
Reset LAM Mask F23A13
Disable LAM F24A15
Enable LAM F26A15

CAMAC FUNCTION DESCRIPTION

  1. A Phase Shift read yields a 16-bit binary number. Phase shift in nsec = 3.100ns*(value of the high bite, i.e. bits 8 through 15) + 0.015ns*(value of the low bite, i.e. bits 0 through 7). If one wants the phase shift expressed as an angle: phase shift in degrees = (3.1ns*(value of the high bite) + 0.015ns*(value of the low bite))*360/18.8ns. For example, 3FF (hexadecimal) is a phase delay of 251 degrees or 13.125 ns.

    The phase shift indicator on the module front panel displays the phase shift in decimal form (in units of 15 psec.); the 3FF above is 1023 on the display.

  2. A Duty Cycle read yields the 8-bit binary value of the duty cycle in percent, for example, 0010111 is 23%. The front panel indicator shows the duty cycle directly in percent.

  3. The coincidence delay can be programmed from 0 to 2047 times the accelerator RF spacing of 19 nsec., i.e. from 0 to 2047 RF buckets of delay (0 to 38.57 usec.). The delay is the lower order 10 bits of the 16-bit RF Delay Word.

  4. The Command word for the RFM module sets the module to use either the internally or externally set coincidence delay and also sets the module in test or normal mode. If bit 0 is set to log '1', the circuitry will use the coincidence delay register for the delay (as set by a Write Coincidence Delay command). If bit 0 is set to '0', the module will use the internal switch setting for the coincidence delay.

    A Command word write with bit 1 set to '0' sets the module into test mode. A second Command Word write with bit 1 set to '1' then starts the test. The module should always return the same value for the phase, and a duty cycle of 25% after the test. Note: Test Mode is disabled during the beam gate (the module returns to normal mode automatically after the test). The Command word can be set or read by CAMAC.

  5. The Module Status Word is used for module diagnostics, set bits indicate:
    Bit Description
    0 Phased Lock Loop circuitry test failure
    1 Duty Cycle circuitry test failure
    2 Module has been set to incorect mode
    3 Module detected no RF input
    4 Module internal RF source is not working
    5 Duty cycle of more than 100% was calculated in error
    6 Remote mode - Uses CATV RF input
    7 Test mode
    8 Local mode - Uses internal RF generator
    9 RF signal (local or remote) is locked to the reference signal
    10...15 Internal status of the duty cycle calculation

  6. The Module Error Word is used for diagnostic purposes.