Motorola MVME166IG/D2 - Manual (Page 25)

Functional Description
MVME166IG/D2 1-11
1
Before you perform any SCSI, VMEbus, or Ethernet I/O with the MVME166,
it may be necessary to define some parameters (e.g., SCSI ID, Ethernet address,
VMEbus mapping). For details on configuring the MVME166, refer to the
setup
command description in Chapter 3 in this manual, and in the
MVME167Bug Debugging Package User’s Manual.
SRAM
The boards include 128KB of 32-bit wide static RAM with onboard battery
backup that supports 8-, 16-, and 32-bit wide accesses. The SRAM allows the
debugger to operate and limited diagnostics to be executed without the
DRAM mezzanine. The SRAM is controlled by the VMEchip2, and the access
time is programmable. The boards are populated with 100 ns SRAMs.
The SRAM is also battery backed up on the MVME166. The battery backup
function is provided by a Dallas DS1210S. The DS1210S supports primary and
secondary power sources. When the main board power fails, the DS1210S
selects the source with the highest voltage. If one source should fail, the
DS1210S switches to the redundant source. Each time the board is powered,
the DS1210S checks power sources and if the voltage of the backup sources is
less than two volts, the second memory cycle is blocked. This allows software
to provide an early warning to avoid data loss. Because the DS1210S may
block the second access, the software should do at least two accesses before
relying on the data.
The MVME166 provides jumpers that allow either power source of the
DS1210S to be connected to the VMEbus +5 V STDBY pin or one cell of the
onboard battery. For example, the primary system backup source may be a
battery connected to the VMEbus +5 V 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.
C
aution
For proper operation of the SRAM, some jumper
combination must be installed on the Backup Power Source
Select Header. If one of the jumpers is used to select the
battery, the battery must be installed on the MVME166. The
SRAM may malfunction if inputs to the DS1210S are left
unconnected.
The onboard power source is a RAYOVAC FB1225 battery which has two
BR1225 type lithium cells and is socketed for easy removal and replacement.
A small capacitor is provided to allow the battery to be quickly replaced
without data loss. The lifetime of the battery is very dependent on the ambient
temperature of the board and the power-on duty cycle. The lithium battery
supplied on the MVME166 should provide at least two years of backup time