Tektronix H600 RFHawk, Service Manual

Page: 48 / 109

Theory of Operation
Table 2-2: Internal ports and buses (cont.)
Internal port, signal, or
bus
Description
Power bus
Supplies power and controls the shut down of individual
instrument modules to conserve battery power.
MODON<4... 1>: 3.3 V CMOS-level signals. An active high
turns on the corresponding instrument module. The module
is MODON1. Only one CMOS load per line is allowed. A low
level on this signal isolates all supplies from the instrument
module. The signal must be active before addressing a
module.
System clock 5 MHz, 3.3 V, TTL-level (SYSCLK) for use by the instrument
module.
Timer signal 3.3 V, TTL-level, implemented in hardware only.
Programmable from 25 ms to 500 ms in 25 ms intervals.
This signal can be used to synchronously accumulate
measurement results to derive time correlated data.
Power System The power system consists of an internal battery charger and power supplies for
the internal boards and instrument module. The Processor board implements
all power management operations. The battery board controls battery charging,
battery selection, and the V
main
value.
Power Management. The platform processor system, peripheral devices, and I/O
implement power management techniques similar to those used in hand-held
HPCs. This includes powering down I/O ports, power supplies, and peripherals
to a shutdown state while running the CPU in sleep mode; power to all circuits
except the real-time clock and the power system micro-controller is turned off.
The power management strategy also includes a screen-saver mode. In this
state, power to the LCD logic and backlight are shut down while maintaining
operation of the I/Os.
The platform uses a non-latching type power switch on the front-panel to
implement power on/off and suspend/resume operations similar to an HPC.
Unlike the HPC however, the platform manages power to the instrument module.
The platform shuts down power to the instrument module by pulling their
respective MODON control signals low and then cutting the power. During power
on from the suspend or shutdown state, the instrument module power supplies are
turned on
fi rst and then the module is turned on using the MODON signals.
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