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The Jorway Model 73A Crate Controller is a double width CAMAC module that interfaces a CAMAC crate to any computer supporting the ANSI standard Small Computer Systems Interface (SCSI) Bus.  Several CAMAC Crates with Model 73A controllers can be intermixed with other SCSI devices on a single SCSI port, which can support up to 7 devices.  The single ended SCSI bus is employed, allowing a maximum bus length of six meters.  The controller has two SCSI-2 high density shielded connectors, allowing devices to be daisy-chained.

The Model 73A obeys all mandatory requirements of the SCSI-2 specification.  All types of CAMAC operations are permitted, including high-speed Block Transfers under hardware control.  Any of three ESONE standard modes can be selected;  Address Scan, Q-Stop or Q-Repeat.  During block transfers, only data is transferred on the SCSI bus.  For any transfer, the user can elect to transfer either two or three data bytes for each CAMAC cycle.  In the latter case, an additional null byte is inserted in the data stream so that 24 bit data is aligned on 32 bit memory boundaries.  The order of byte transmission is user selectable as high order first or low order first.  The Model 73A can be operated in synchronous as well as asynchronous SCSI mode, and can transfer data at full dataway speed.

Modules asserting LAM's (Look-At-Me's) can interrupt the computer using the SCSI Asynchronous Event Notification (AEN) protocol.  In the course of this protocol, the complete pattern of asserted LAM's from a single crate is transferred to the host, which can determine the crate ID during the selection process.  Note that the host adapter must be capable of operating in target mode to use this protocol.  In other respects, the Model 73A provides the same functionality as the Type A CAMAC controller, including the Station Number Register, and uses the same codes for commands addressed to the controller itself.  Therefore, the Read-L command can be used to poll for LAM's.  In addition, the Model 73A incorporates a LAM mask register.

73A Specifications
R/G On Indicator Illuminated when Request/Grant Arbitration is set ON internally
D Indicator Illuminated when one or more Look at Me demands (GL's) are present.
I Indicator Illuminated wherever Dataway Inhibit is at a Logic 1.
Crate Address Front Panel thumb wheel.  Positions 0 to 7.  Signifies current SCSI address.
On Line/Off Line Two position locking switch.  Determines if controller will execute CAMAC commands.  Unit will respond to SCSI command but return an error status to the host when in the OFF LINE position and CAMAC commands are attempted.
Z/C Two position momentary contact switch.  Active only in the OFF LINE state.  Manual C affects only the CAMAC modules, and does not change the internal state of the controller.  Manual Z initializes all CAMAC modules as well as the controller.  Equivalent to Power-On Reset.  Sets Dataway inhibit, disables LAM's, and establishes the SCSI UNIT ATTENTION condition. The controller can be switched OFF LINE and the manual Z switch actuated at any time, without causing SCSI protocol errors, as the action is delayed until the controller is idle.   Manual Z should be used if the controller's SCSI ID has been changed while the crate is powered, so the new ID is recognized.  Manual Z does not affect other devices on the SCSI bus.
The SCSI Standard does not provide for a device like a CAMAC crate.  Therefore, non-Standard Command Descriptor Blocks are used, following the IDENTIFY message of the SCSI-2 specification.  Both 6 and 10 byte commands are used, the latter only for block data transfers of 256 or more bytes in length.
+6V 1500mA
-6V 30mA
NOTE: Maximum current requirements are worst case values. +6v and -6v worst case do not exist at same time. Actual currents will range up to maximum depending upon type of operation and duty cycle. Maximum Power is less than 10 watts under all conditions.

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