Accelerator Development Department / RHIC Project
Associated Universities Inc.
Brookhaven National Laboratory
Upton, New York 11973


RHIC Real Time Data Link System
July 13, 1993 edited October 24, 1996
H. Hartmann

1.0 Introduction
1.1 Frame Protocol
2.0 V105 Encoder Module
3.0 V106 Input Module

1.0 Introduction

The Rhic Real Time Data Link (RTDL) distributes to all locations around the RHIC ring machine parameters of general interest to accelerator systems and users. Defined parameters include, but are not limited to, the following:

  1. Programmed Blue Ring Current
  2. Programmed Blue Ring Current Dot
  3. Measured Blue Ring Current
  4. Measured Blue Ring Current Dot
  5. Programmed Yellow Ring Current
  6. Programmed Yellow Ring Current Dot
  7. Measured Yellow Ring Current
  8. Measured Yellow Ring Current Dot

The RTDL System is comprised of two module types: the V105 Encoder and the V106 Input. There is only one encoder module, but many (up to 128) input modules. The RHIC RTDL system will be located in the 4 o'clock service building (1004B). The V105, V106's and supporting host computer interface (FEC) are packaged in standard 6U VME format.

RTDL system distribution is point-to-point differential TTL on shielded twisted pair wire. The V105 is isolated from the receiving modules by transformer coupling at the receiving modules input. The V105 initially drives a fanout/repeater module which provides multiple buffered TTL differential outputs. These outputs will be used locally within 1004B, and others will drive fiber optic transmitters for optical transmission to other RHIC equipment locations. At each RHIC equipment location, the optical transmission is received, regenerated (restoring waveshape and timing), and buffered as differential TTL. A fanout/repeater is utilized to generate multiple outputs. General purpose V108 Utility modules which
receive the RTDL frames may be located in these areas, as well as specially designed modules such as the V115 waveform generator, having direct RTDL inputs.

RTDL parameter frames are transmitted using a serial modified Manchester code (bi-phase mark). Each frame has the following format:

1.1 Frame Protocol

|----------------------------------------------------------------------|

| 0 | MSB-Parameter ID - LSB | MSB -Parameter Data - LSB | P | 1 |

The transmission rate is 10Mb/s and 3.5us are required to transmit each parameter frame. All defined frames are transmitted at each occurance of the 720Hz event on the RHIC Event Link. The RTDL encoder module transmits a continuous bi-phase mark "one" (10MHz carrie) during idle periods.
RTDL parameter frames are permanently assigned a parameter ID code. The RTDL encoder module contains a record of all defined parameter ID codes. RTDL parameter transmission priority is defined in the V105 scan list RAM.

2.0 V105 ENCODER MODULE

2.1 Theory of Operation

The RHIC Real Time Data Link (RTDL) V105 Encoder Module is a standard VMEbus 6U module. It occupies 4HP of a standard 84 HP VME chassis. This module directly outputs the encoded machine parameters onto the link. It accepts data from the V106 Dual Channel Input Module. Data is accepted into the V105's transmit register at a rate solely determined by the handshaking protocol initiated by the V105. The V105 Module converts each machine parameter acquired from the V106 Modules into a serial bi-phase mark coded frame for transmission. Under normal operation, the V105 Module will receive a TRIGGER TRANSMITTER signal from the 720 Hz event on the RHIC Event Link. However, for RTDL System diagnostic purposes, two other options are available:

At the selected trigger, the following will occur:

  1. The on board memory which has been loaded with the RTDL parameter IDs to be transmitted will be enabled. This parameter ID will be available for all input modules to read via a local bus.
  2. The Address Strobe signals that a valid parameter ID has been placed on the bus.
  3. All input module channels decode the parameter ID.
  4. The channel whose parameter ID matches the one placed on the bus places its machine parameter on the bus.
  5. The DaTa ACKnowledge Strobe signals the encoder module that valid machine parameter ID data has been placed on the bus.
  6. The bi-phase mark encoder is triggered and the data is transmitted as one frame.
  7. This process continues until all defined frames have transmitted.

If the DaTa ACKnowledge Strobe is not received by the encoder module within 1 us of its asserting the Address Strobe, an interrupt will be generated. The Parameter ID of the nonresponsive channel (NOREPLY) will be stored in the status register.

2.2 VMEbus Specifications

The Encoder Module is a VMEbus slave and adheres to the following protocol:

2.2.1 VMEbus Address and Data

  1. VMEbus address capability: A16
  2. VMEbus data capability: D16/D08(EO) (Ram D08(EO) only)
  3. Block and read-modify-write transfers are not allowed.

2.2.2 VMEbus accessible registers

  1. 64-bytes organized as 32 16-bit words of Status/ID.(non-volatile)
  2. 2-byte status register.
  3. 2-byte command register.
  4. 2-byte interrupt vector register.

2.2.3 VMEbus interrupts generated if

  • 1. The addressed Input Module Channel does not respond when polled.
  • 2. Event Link Carrier not detected.

    • 2.2.4 VMEbus interrupt Service

  • 1. Provides an 8-bit status/ID reply byte. This byte is set by the FEC. (Front End Computer)
  • 2. Interrupt level is user selectable via the FEC. (including no interrupts)
  • 3. The interrupt is released when the interrupt status register is read. (RORA)

    • 2.3 Front Panel

    2.3.1 Indicators

    2.3.2 Connectors

    3.0 V106 INPUT MODULE

    3.1 Theory of Operation

    The RHIC Real Time Data Link (RTDL) V106 Input Module is a standard VMEbus 6U module. It occupies 4HP of a standard 84 HP VME chassis. Each module has two channels. Data input is a serial link bit stream received via front panel fiber optic ST connectors . Data can also be loaded via the VMEbus by the FEC. Machine Parameter Data is loaded into the output register on the occurrence of the LDDATA strobe from the V105 Module. This strobe is synchronous with triggering of the V105 Module. The V106 Modules are connected via a VMEbus P2 connector user defined bus. This bus terminates at the 105 Module. When the Encoder Module places a Parameter ID on the bus, the following happens:

    1. All Input Module channels decode the Parameter ID with the occurrence of the Address Strobe.
    2. The channel that decodes a match places its output register data on the bus and the DaTa ACKnowledge strobe is asserted.
    3. Bus cycles continue until all channels have been polled.

    3.2 VMEbus Specifications

    The Input Module is a VMEbus slave and adheres to the following protocol:

    3.2.1 VMEbus Address and Data

    1. VMEbus address capability: A16
    2. VMEbus data capability: D16/D08(EO)
    3. Block and read-modify-write transfers are not allowed.

    3.2.2 VMEbus accessible registers:

    1. 64-bytes organized as 32 16-bit words of Status/ID. (non-volatile)
    2. 2 2-byte status registers. One for each channel.
    3. 2 2-byte command registers. One for each channel.
    4. 2 4-byte VME Data Registers. One for each channel.
    5. 2 4-byte Device Data Registers. One for each channel.

    3.2.3 VMEbus interrupts generated if

    3.2.4 VMEbus Interrupt Service:

    Parameter ID is jumper selectable and available to the FEC via the status register.

    3.3 Front Panel

    3.3.1 Indicators

    1. Channel 1
    1. Channel 2
    1. VME SEL - Board Addressed by FEC - Green Led

    3.3.1 Connectors