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Theory of Operation
2715 Spectrum Analyzer Service Manual
3-75
The Real Time Clock (RTC) is an Oki Semiconductor MSM62X42BRS
clock/calendar (U23). This IC uses an internal 32,768 Hz clock which is divided
down to 1 Hz. This one hertz clock is then used to drive the time registers. Each
time register consists of some multiple of ten of the current time (i.e. 1 sec, 10
seconds, 1 minute, 10 minutes, ..., 10 years). The time registers are also
writeable allowing easy time setting. The data bus for this part is only 4 bits
wide and connected to bits 0 to 3 of the microprocessor data bus. The real time
clock circuitry has a battery backup. Table 3--25 shows the Real Time Clock
functions.
Table 3- 25: Real Time Clock Functions
Register Name Address Access Type
Seconds 0x00300 R/W
Seconds x 10 0x00301 R/W
Minutes 0x00302 R/W
Minutes x 10 0x00303 R/W
Hours 0x00304 R/W
Hours x 10 0x00305 R/W
Days 0x00306 R/W
Days x 10 0x00307 R/W
Months 0x00308 R/W
Months x 10 0x00309 R/W
Years 0x0030a R/W
Years x 10 0x0030b R/W
Day of week 0x0030c R/W
Control Register D 0x0030d R/W
Control Register E 0x0030e R/W
Control Register F 0x0030f R/W
The EPROM consists of a single 32 pin socketed 27C200 (U5).
The nonvolatile RAM allows the storage of waveforms and instrument settings.
It consists of a single 128k by 8 CMOS SRAM (U8). Only 96 K of this device is
addressable due to display storage allocations. The battery backup circuit
provides the nonvolatility of this RAM.
Real Time Clock
EPROM
NVRAM