System Monitor Functions; Reset; System Clock Driver; Vmebus Arbiter - Performance Computer PT-VME161 User Manual

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Section FUNCTIONAL DESCRIPTION

System Monitor Functions

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44 Extensible Single Board Computer/Controller User's Manual
The SCV64 is capable of providing VMEbus System Controller functions. These include Bus
Arbitration, System Clock Driver, IACK Daisy Chain Driver and Bus Timer. The PT-VME161
does not generate the AC Failure detection feature of the VMEbus Power Monitor [ACFAIL*]
however, it is capable of monitoring the signal. The VMEbus Serial Clock Driver functions are
not provided.
The SCV64 samples the VMEbus signal [BG3IN*] shortly after the PT-VME161 detects a
power on condition and on every negating edge of VMEbus [SYSRST*]. If [BG3IN*] is low,
the SCV64 enables itself as the VMEbus System Controller. The System Controller functions
will be enabled automatically if the PT-VME161 is in slot 1 and [BG3IN*] is open. Software
can determine if this has occurred by reading the SYSC status bit of the SCV64 Status Register
1.
CAUTION: The PT-VME161 requires that the card preceding in the bus grant daisy chain
adhere to the IEEE 1014 (VMEbus) rule that requires all Bus Grant outputs to be driven high
during reset. If the preceding card is driving [BG3OUT*] low at the end of reset, a system
malfunction could result.

Reset

The VMEbus [SYSRST*] signal can always be driven by the SCV64, whether or not it is
the System Controller. There are three conditions under which [SYSRST*] is driven: the
PT-VME161 detects a power on condition, VMEbus [BG0IN*] is asserted (while System
Controller), or software sets the SWRST bit in the SCV64 General Control Register.

System Clock Driver

If the PT-VME161 is the System Controller the 16 MHz, 50% duty cycle [SYSCLK] signal
will be generated on the VMEbus.

VMEbus Arbiter

Only enabled when the PT-VME161 is the System Controller, the VMEbus Arbiter
provides four programmable arbitration schemes along with arbitration time-out.
The arbitration mode is determined by the ARB1 and ARB0 bits in the SCV64 VMEbus
Arbiter Register. The possible modes are: Full Round Robin. Bus Request Level 3 has
priority over levels 2, 1, and 0 which are handled in Round Robin mode. Bus Request
Levels 3 and 2 have priority over levels 1 and 0 which are handled in Round Robin mode.
And, full Priority mode.
Arbitration time-out is enabled by the ATEN bit in the SCV64 VMEbus Arbiter Register.
The Bus Grant issued by the arbiter will be withdrawn after 16 us, if no card asserts BBSY*
to take ownership of the VMEbus. The arbiter then waits 16 us to allow the deasserted grant
to fully propagate through the daisy chain, then rearbitrates the bus.

IACK Daisy Chain Driver

The IACK Daisy Chain Driver (DCD) performs the standard VMEbus System Controller
IACK DCD function, as well as providing the VMEbus Interrupt Generator logic.