Service manual

System Overview 1-43

A single Alpha processor chip is on the CPU module.

Some features of the CPU module are:

• QBB system interface

• PSM interface, both I

C and serial I/O

• Backup cache of 4 Mbytes

• Master phase lock loop (MPLL) clock (reference supplied by the QBB backplane)

• On-board DC-DC converter (48V to a voltage specific to the CPU chip) (other than

the power modules this is the only module in a QBB to have a 48V input)

• Short-circuit protection

• On-board SROM for diagnostics

• Module hot-swap (PSM control for power-on and power-off)

• Two LEDs:

Hot Swap OK – Yellow – normally off

Run – Green – normally on

• I

C bus 8-bit expander register for module status

• I

C bus EEPROM containing module serial number, B-cache size, QSA parameter

bit, and FRU error information relevant to the module

Table 1– 9 CPU Variants

Module Variant Cache Size Base CPU

B4125-Ax 4 Mbytes EV67