HYDRA

Service Manual

the WE* signal is low, NAND gate output A6U2-3 goes high to latch the data bus into the lower part of the page register (A6U1).When register select PAGEH goes high and the WE* signal is low, NAND gate output A6U2-8 goes high to latch the lower three bits of the data bus into the high part of the page register (A6U4).

2-75. Byte Counter

The Byte Counter is a seven-bit ripple counter that controls the lower address bits of the nonvolatile RAMs. This counter is cleared when a new value is written to the lower page register. It automatically increments at the end of each read or write access to the memory data register.

NAND gate output A6U2-3 goes high to write the lower page register and clear the Byte Counter. When data is read from or written to the Non-Volatile Memory, NAND gate output A6U2-6 goes high during the memory cycle, and then low at the end of the memory cycle. The transition from high to low increments the Byte Counter so that the next access to the memory data register will be for the next sequential byte in the Non- Volatile Memory.

2-76. Nonvolatile Memory

The Non-Volatile Memory is made up of two 128K-byte static CMOS memories with integrated lithium battery, power-fail detection, and battery switching circuitry. When the VCC (+5.1V dc) power supply is above +4.5V dc, memories A6U6 and A6U7 are fully operational. When VCC drops below approximately +4.25V dc, all access to the memory are disabled by the internal power-fail detection circuit. When VCC drops below about +3.0V dc, the battery switching circuitry disconnects VCC and connects the lithium battery to the memory so that data is retained while the instrument power is off.

The most significant bit of the Page Register (A6U4-1,16) is gated with the MEMORY register select signal by A6U5 to get the memory chip select signals (A6U5-6 and A6U5-8). Memory pages 0 through 1023 are stored in memory device A6U7, and memory pages 1024 through 2047 are stored in memory device A6U6. The WR* and RD* control signals from the Microprocessor on the Main PCA are used to enable writing of data to and reading data from the memory devices, respectively.

2-77. IEEE-488 Interface (Option -05)

Refer to Section 7 for detailed circuit description of this option.

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Fluke 2635A, 2625A service manual IEEE-488 Interface Option
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2635A, 2625A specifications

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