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NetDAQ
Service Manual
2-18
Flash Memory
2-35.
The Flash EPROM is an electrically erasable and programmable memory that provides
storage of instructions for the Microprocessor and measurement calibration data.
A switching power supply composed of A1U12, A1L3, A1CR16, A1C11, A1C15,
A1C86, and A1C97 generates a n12 volt programming power supply (Vpp)
when the Microprocessor drives VPPEN high (A1U12-2). Resistor A1R119 pulls
A1U12-2 to near ground during power-up to ensure that A1U12 is not enabled while the
Microprocessor is being reset. When the power supply is not enabled, the output voltage
(Vpp) should be about 0.1 volt less than the input voltage of the power supply (Vcc).
The only time that the programming power supply is active is when new firmware is
being loaded or new calibration constants are being stored into the Flash EPROM. The
code executed immediately after power-up is stored in an area of the Flash EPROM
(known as the Boot Block) that is only erasable and reprogrammable if BBVPP
(A1U21-44) is at a n12 volts. This may be accomplished by installing jumper
A1W2, but this should only be done by a trained technician, and A1W2 should never be
installed unless it is necessary to update the Boot firmware. In normal operation, resistor
A1R124 and diode A1CR20 pull BBVPP up to about 0.25 volts less than Vcc.
The FLSH* chip select (A1U1-128) for this device goes low for any memory access to
A1U21. The FLSH* signal goes through jumper W3, which must always be installed
during normal instrument operation. W3 is removed only during the initial programming
of the Flash Memory during production at the factory.
Static RAM
2-36.
The Static RAM (SRAM) provides 512K bytes of data storage for the instrument using
128Kx8 SRAM devices. The board may also be configured for 2M bytes of data storage
using 512Kx8 SRAM devices.
The RAM* address decode output (A1U1-127) for the SRAM goes low for any memory
access to A1U20, A1U30, A1U34, or A1U35. Two OR gates in A1U15 are used to select
two of the memory chips. RAM1* selects A1U20 and A1U30, and RAM2* selects
A1U34 and A1U35. A1R125 or A1R126 is installed depending on the size of the
memory chips. A1R125 is installed for 128Kx8 SRAMs, or A1R126 is installed for
512Kx8 SRAMS. Address bit 18 (A18) is inverted to A1U20-30 and A1U30-30 to
provide an active high chip select when 128Kx8 SRAM chips are used.
A1U30 and A1U35 are connected to the high 8 bits of the data bus, so read accesses are
enabled by the Read Upper (RD1*;A1U30-24;A1U35-24) signal going low, and write
accesses are enabled by the Write Upper (WRU*;A1U30-29;A1U35-29) signal going
low. A1U20 and A1U34 are connected to the low 8 bits of the data bus, so read accesses
are enabled by the Read Lower (RD2*;A1U20-24;A1U34-24) signal going low, and
write accesses are enabled by the Write Lower (WRL*;A1U20-29;A1U34-29) signal
going low.
Содержание NetDAQ 2640A
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Страница 218: ...NetDAQ Service Manual 6 14 2645A 1601 Figure 6 2 A1 Main PCA Assembly...
Страница 220: ...NetDAQ Service Manual 6 16 2620A 1601 Figure 6 3 A2 Display PCA Assembly...
Страница 225: ...List of Replaceable Parts Parts Lists 6 6 21 2640A 1603 Figure 6 4 2640A A3 A D Converter PCA Assembly...
Страница 230: ...NetDAQ Service Manual 6 26 2645A 1603 Figure 6 5 2645A A3 A D Converter PCA Assembly...
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Страница 242: ...2640A 2645A Service Manual 7 10 Figure 7 2 A2 Display PCA Assembly 2620A 1602...
Страница 243: ...Schematic Diagrams 7 7 11 Figure 7 2 A2 Display PCA Assembly cont 2620A 1002...
Страница 244: ...2640A 2645A Service Manual 7 12 2640A 1603 Figure 7 3 2640A A3 A D Converter PCA Assembly 2640A 1603...
Страница 251: ...Schematic Diagrams 7 7 19 2645A 1603 Figure 7 4 2645A A3 A D Converter PCA Assembly 2645A 1603...
Страница 258: ...2640A 2645A Service Manual 7 26 Figure 7 5 A4 Analog Input PCA Assembly 2620A 1604...
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