User guide

Table 9–12 lists the register and memory addresses for the keyboard/mouse
controller.
Table 9–12 Keyboard and Mouse Controller Addresses
Offset Physical Address Register
60-R 1 C000 0C00 Auxiliary/keyboard data
60-W 1 C000 0C00 Command data
64-R 1 C000 0C80 Read status
64-W 1 C000 0C80 Command
9.6 TOY Clock
The TOY clock function maintains the timekeeping information: year, month,
date, day, hour, minute, second, 1/10th of a second, and 1/100th of a second. The
date is corrected for months with fewer than 31 days and for leap years. The
time can be maintained in 24-hour format or 12-hour with AM/PM format. The
time is stored in binary code decimal (BCD). For example, a time of 29 minutes is
stored in location (TOY_BASE_ADDR+02) as 0x29.
A Dallas Semiconductor DS1386 chip is used to implement the TOY clock but
does not support the chip’s alarm features. This chip also maintains the watchdog
timer and SRAM functionality, described in Sections 9.8 and 9.9.
The square wave output of the chip generates a fixed 1024 Hz interval interrupt.
Timekeeping accuracy is better than +/-1 minute/month at 25°C.
Timekeeping is maintained in the absence of Vcc by an internal lithium energy
cell, which has an active life of at least 10 years. In addition, the device
internally protects against spurious accesses during power transitions. Some
applications may require the TOY clock (and SRAM) to operate from an external
uninterruptable power supply (UPS). Digital Alpha VME 4 has an onboard switch
(J3 switch 1) to allow a connection to the 5 V standby connection on the VMEbus
(5VSTDBY). When switch 1 is closed, VME 5VSTDBY is connected to the TOY
clock supply through isolation diodes.
The chip is socketed to allow:
• Replacement when the internal power source is no longer functional
• Physical removal of the NVRAM
The TOY clock timekeeping registers are updated every 0.01 seconds. Access
to the TOY clock, to examine or set current time, is by nine registers: the
timekeeping registers and the command register.
9–22 Nbus