RELIANCE 45C961 Power interface module

The DRAM map decoder may be programmed to accommodate different base address(es) and sizes of mezzanine boards. The onboard DRAM is disabled by a local bus reset and must be programmed before the DRAM may be accessed. Refer to the MC2chip and MCECC descriptions in the MVME172 VME Embedded Controller Programmer’s Reference Guide for detailed programming information.Most DRAM devices require a certain number of access cycles before the DRAMs are fully operational. Normally this requirement is met by the onboard refresh circuitry and normal DRAM initialization. However, software should insure a minimum of 10 initialization cycles are performed to each bank of RAM

SRAM Options

 The MVME172LX provides 128KB of 32-bit-wide onboard static RAM in a single non-interleaved architecture with onboard battery backup. The SRAM arrays are not parity protected. The battery backup function for the onboard SRAM and the mezzanine SRAM is provided by an Electro Marketing EM1275 device (or equivalent) that supports primary and secondary power sources. In the event of a main board power failure, the EM1275 checks power sources and switches to the source with the higher voltage. If the voltage of the backup source is lower than two volts, the EM1275 blocks the second memory cycle; this allows software to provide an early warning to avoid data loss. Because the second access may be blocked during a power failure, software should do at least two accesses before relying on the data.

The MVME172LX provides jumpers

 (on J14) that allow either power source of the EM1275 to be connected to the VMEbus +5V STDBY pin or to one cell of the onboard battery. For example, the primary system backup source may be a battery connected to the VMEbus +5V STDBY pin and the secondary source may be the onboard battery. If the system source should fail or the board is removed from the chassis, the onboard battery takes over. ! Caution For proper SRAM operation, some jumper combination must be installed on the Backup Power Source Select header (refer to the jumper information in Chapter 1). If one of the jumpers is set to select the battery, a battery must be installed on the MVME172LX. The SRAM may malfunction if inputs to the EM1275 are left unconnected.

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