4-4
4
A table in the Flash memory chip contains all of the 4867’s configuration
settings, serial number and other parameters that are subject to change. At
power on time or when the external reset input is pulled to ground, the power
supervisor resets the Digital I/O direction latch, the microprocessor and the
GPIB interface chip. When the reset is released, the microprocessor
performs its selftest and copies the configuration from Flash memory to
RAM memory where it is used to operate the unit.
The RAM copy of the configuration table is continually updated as the 4867
receives new commands. Any changes to the configuration settings are not
stored in the Flash memory until the unit receives the *SAV command. The
RAM is a 32K x 8 static memory that is used to hold the operating variables
and configuration settings. All data stored in the RAM memory is lost when
power is turned off..
Regulated DC power to run the 4867’s internal logic chips is supplied
directly from the power supply. The power supply is a high-frequency
switching buck regulator that converts unregulated 9 to 32 Vdc into
regulated 5 Vdc power. Due to the use of CMOS circuits, the 4867's power
consumption is very low. Less than 250 mA is consumed when the outputs
are unloaded. A separate charge pump converter generates
±
9.3 Vdc
voltages to power the analog circuits.
The 4867 has six front panel LEDs that show the unit's current status. The
LEDs are pulled low when the drive signals are active. A 1500 ohm series
resistor limits the LED drive current to 2.6 mA. A header is provided on the
4867 and 2367 to operate a remote set of LEDs.
On OEM board versions of the 4867, headers are provided for GPIB, LED
and optional serial interfaces. The standard right-angle GPIB connector is
replaced on OEM boards by a header which also includes signals to sense
an external GPIB address switch. Power connections are made to a two-
screw terminal block adjacent to the power supply.
