Agilent Technologies E3631A manual Theory of Operation Floating Logic

Chapter 4 Theory of Operation

Floating Logic

Floating Logic

Referring to the schematic shown on page 128, the floating common logic controls operation of the entire instrument. All output functions and bus command interpretation is performed in the main controller U17. The front panel and the earth referenced logic operate as slaves to U17. The floating common logic is comprised of the main controller U17, custom gate array U16, the program ROM U14, RAM U15, calibration EEPROM U18, and the 12 MHz clock oscillator Y1 on the top board . Non-volatile EEPROM U18 stores calibration constants, calibration secure code, and calibration count. Power- on reset is provided to the main controller by the voltage regulator U1 on the top board.

The main controller U17 is a 16-bit micro controller. It controls such features as receive and transmit serial port, timer/counter ports, an 8-bit pulse width modulated DAC port, and selectable input 10-bit successive approximation a- to-d convert ports. A conventional address/data bus is used to transfer data between the main controller and external ROM and RAM. When the address latch enable (ALE) signal goes high, address data is present on the address/ data bus. ASIC U16 latches the address data and decodes the correct chip enable (low true) for external ROM and RAM accesses and for read/write accesses to the internal registers of U16. The system memory map is shown below.

0000H - 1FF7H	U15	8k x 8 RAM
1FF8H - 1FFFH	U16	Gate Array
2000H - FFFFH	U14	Program ROM

Program ROM U14 contains four 64k x 8 data banks of data. Banks are selected by controlling A16 and A17 ROM address bits directly from the main controller port bits.

Custom gate array U16 performs address latching and memory map decoding functions as discussed above. In addition, U16 contains a variety of internal read/write registers. The read (XRD) and write (XWR) signals transfer data out of and into U16 when it is addressed. There are four internal registers in U16: an internal configuration register, an 8 bit counter register, a serial transmit/ receive register, and an internal status register.

The counter register is used to capture the ADC slope count at the COMP input. The COMP input functions as both a clocked comparator and the slope counter input for the ADC. In both cases the counter register captures the lower 8 bits of a 24-bit counter. The upper 16 bits of the count are captured by the SYNC input to U17.

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