Motorola MCPN750A Hot Swap Control Circuitry, Programmable Timers, Raven General Purpose Timers

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Functional Description

Hot Swap Control Circuitry

The MCPN750A provides CompactPCI Hot Swap capability and complies with the CompactPCI Hot Swap Specification (Rev. 1.0). The Hot Swap circuitry supports the process of installing or removing the board without adversely effecting the running system.

The Hot Swap circuitry consists of the Linear Technology LTC1643 controller along with some external FETs and discrete components. The two external N-channel FETs control the +5V and +3.3V supplies while on-chip switches control the +12V and -12V supplies. All supply voltages are increased at a controlled rate. An electronic circuit breaker protects all four supplies against over-current faults.

A switch, located in the lower ejector handle, is used to signal the insertion or impending removal of the board. The state of this switch is monitored by the 21554 bridge chip which will assert the CompactPCI ENUM# signal. The ENUM# signal indicates to the System Controller board either that the board has been inserted and is ready for configuration or that the board is about to be removed. A blue LED is provided on the front panel to indicate when it is safe to remove the board from the chassis.

Programmable Timers

Among the resources available to the local processor are a number of programmable timers. Timers and counters on the MCPN750A are provided by the Raven ASIC, the M48T559 and, the PBC . They can be programmed to generate periodic interrupts to the processor.

Raven General Purpose Timers

The Raven ASIC contains four 31-bit general purpose timers. Each timer is driven by a divide-by-eight prescaler which is synchronized to the PPC processor clock. For a 66.66 MHz system, the timer frequency would be 8.25 MHz. Each timer may be programmed to generate an MPIC interrupt.

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