VME-SG Microchip Timing Module

The Microchip / TrueTime VME-SG is a precision time source that conforms with the IEEE 1014.C-1 VMEbus Specification. The VME-SG operates in one of the following three modes: Generator, GPS Synchronized Generator (GPS-VME only) or Code Synchronized Generator. In all modes the VME-SG is designed to supply precise time to a VME based computer. The time consists of microseconds through thousands of years. In the Generator mode the time can be started, stopped and preset via the VME bus. The Generator counters can also be started using an external reference 1 PPS pulse. In the GPS Synchronized Generator mode the card operates with the GPS Engine. Time and position are derived from the NAVSTAR Global Positioning System (GPS). In the Code Synchronized Generator mode the generator will phase lock to an external IRIG B time code. The code format can be either amplitude modulated or DC shift at RS-422 logic levels. In all synchronized modes the internal oscillator is disciplined to remove any frequency offset with respect to the external reference. This is necessary to maintain precise phase lock and to minimize drift error if the input reference is lost.

Time information and status are available to the VME computer bus in five, 16 bit words. Each word contains up to 4 packed BCD time values. Since no time ready flags must be set before time information can be read, the data is immediately available (zero latency). On board DIP switches select the memory address space where the VME-SG board resides.

Two independent time capture register sets are provided. Time is latched or "frozen" in one set of registers by a user read operation via the VME bus. This will provide time on request. The second set of capture registers has the time latched into it when an External Event pulse occurs. This allows time tagging of an External Event. An event normally is programmed to generate an interrupt to flag its occurrence.

A Rate Generator is provided that is configured by the user to output one of 5 different pulse rates to the P2 connector. The Rate Pulse can also be configured to produce an interrupt to the VME processor.

Two Time Compare register sets are available that are preset with time values from hundreds of days through microseconds via the VME bus. When either compare time is equal to the generator time an output pulse is generated.

Four independently programmable interrupts are available each with software selectable priority. The interrupt sources are the External Event, Rate Pulse, Time Compare 1 and Time Compare 2.

The VME-SG is configured as an A16/D16 slave board responding to the Address Modifier codes hex 29 (short non-privileged) and hex 2D (short supervisory). The VME-SG is memory mapped on any 256 byte boundary of the VME bus short address space using the eight position DIP switch located on the board.