Microprocessor Bus &
Interfaces
The instrument has a conventional 16-bit mic roprocessor bus
with 16 bits bidirectional data signals, 5 bits address signals,
Chip Selects and wrn and rdn signals. It connects the proces-
sor to the FPGA, the GPIB and the USB. See Figure 6-34.
The FPGA connection has 16 data bits, 5 address bits, chip
select, wrn and rdn. The FPGA is controlled by the processor
via the bus. Measuring f unctions are selected, f or instance.
The FPGA is controlled between each measurement or block
of measurements. An interrupt signal from the FPGA is con
-
nected to the processor. See Figure 6-36 for a typical timing
diagram.
The connection to the USB has 16 data bits, 1 address bit, chip
select, wrn and rdn. An interrupt signal from the USB IC is
connected to the processor. See Figure 6-38 for a typical tim
-
ing diagram. The USB IC is a complete USB unit. It is not
powered from the USB bus. The USB IC (U34) has a 6 MHz
oscillator. Check at C416.
The connection to the GPIB has 8 bits, 5 address bits, chip se
-
lect, wrn, rdn and a special control signal for the level shifting
IC (U38). U38 is a buffer between the logic level of +3.3 V for
the processor and the logic level of +5 V for the GPIB IC
(U37). An interrupt signal from the GPIB IC is connected to
theprocessor.Seefigureeeforatypicaltimingdiagram.The
GPIB IC is a complete GPIB unit. The GPIB IC (U37) has a
40 MHz oscillator. Check at TP20.
Only the selected interface is involved in communi cat i on on
the microprocessor bus.
Troubleshooting 6-21
Figure 6-29 LCD control signals, oscillogram #6.
Figure 6-30 Keyboard interrupt.
LD
RESETN
RAN
FRM
D3
D1
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