Theory of Operation (2635A) 2A

Detailed Circuit Description

Clock Dividers

The 12.288-MHz system clock (A1U25-30) is divided down by the Clock Dividers to create the 3.072-MHz Option Clock (OCLK; A1U25-22) and 1.024-MHz Display Clock (DCLK; A1U25-19). The Display Clock is not a square wave; it is low for 2/3 of a cycle and high for the other 1/3. The Display Clock is also used internal to the FPGA to create the 128-kHz Totalizer Debouncer Clock and the 4-kHz Keyboard Scanner Clock.

Internal Register Address Decoding

The FPGA logic decodes four bits of the address bus (A<3> through A<6>), the PGA* chip select signal (A1U25-88), RDU* (A1U25-95), and WRU* (A1U25-5) to allow the Microprocessor to read five registers and write to three registers implemented in the FPGA logic. The absolute addresses are listed in Table 2A-1.

Keyboard Scanner

The Keyboard Scanner sequences through the array of switches on the Display Assembly to detect and debounce switch closures. After a switch closure is detected, it must remain closed for at least 16 milliseconds before the Microprocessor will be interrupted and the Keyboard Input register will be read from the FPGA. When the keyboard interrupt (KINT*, A1U25-62) goes low, the Keyboard Scanner stops scanning until the Microprocessor reads the Keyboard Input register which automatically clears the interrupt by driving KINT* high again. The FPGA will interrupt the Microprocessor again when the switch on the Display Assembly is detected as open again. Actually the Microprocessor will be interrupted once for each debounced change in the contents of the Keyboard Input register. See also the information on "Front Panel Switches" in the "Display PCA" section for this instrument.

The Microprocessor can enable or disable the Keyboard Scanner by changing the state of a bit in the Control/Status register that is in the FPGA. The Keyboard Scanner is disabled if the instrument is in either the RWLS or LWLS state (see User Manual; RWLS and LWLS Computer Interface Commands).

Digital I/O Buffers and Latches

The FPGA logic implements internal registers for the eight Digital Outputs (DO<0> through DO<7>) and the four Alarm Outputs (AO<0> through AO<3>). These registers are both written and read by the Microprocessor. The FPGA logic also implements an eight-bit input buffer so that the Microprocessor can read the eight Digital Input lines (DI<0> through DI<7>). See also "Digital Input Buffers" and "Digital and Alarm Output Drivers".

Totalizer Debouncing and Mode Selection

Logic internal to the FPGA lets the Microprocessor enable a debouncer in the Totalizer input signal path. The detailed description of the Totalizer Debouncer and Mode Selection may be found under the heading "Totalizer Input".

External Trigger Logic

Logic internal to the FPGA allows the Microprocessor to set up the External Trigger Logic to interrupt on rising or falling edges of the XTI input to the FPGA. The detailed

2A-17

Page 98 Page 100
Page 99
Image 99
Fluke 2625A, 2635A service manual Clock Dividers
Page 98 Page 100

2635A, 2625A specifications

The Fluke 2625A is a sophisticated data logger designed for a wide range of industrial and laboratory applications. This versatile instrument excels in capturing and monitoring temperature and voltage measurements with precision and reliability. One of its standout features is its ability to record data from various sensors, making it ideal for environments where comprehensive data acquisition is critical.

Equipped with a large LCD display, the Fluke 2625A provides clear and user-friendly access to real-time measurement data. Its graphical interface allows users to visualize trends and monitor readings easily, which significantly enhances usability. The device supports a variety of input types and can connect to thermocouples, RTDs, and other sensors, offering great flexibility for various measurement tasks.

The Fluke 2625A employs advanced measurement technologies that ensure accuracy in data logging. With a high sampling rate, it captures fast-changing signals while maintaining data integrity. The device features a built-in memory that allows for extensive logging, accommodating long-term monitoring tasks without requiring constant oversight. Users can set it to log data at specified intervals, offering customizable solutions for different monitoring needs.

Another significant characteristic of the Fluke 2625A is its robust communication capabilities. The device supports USB and RS-232 interfaces for easy connectivity with computers and other devices, making data transfer and analysis seamless. This feature is especially beneficial for users who need to compile or analyze large sets of data quickly.

Furthermore, the Fluke 2625A is designed with durability in mind. Its rugged construction makes it suitable for challenging environments, including those with high levels of vibration, dust, or moisture. This reliability ensures that the device can withstand the rigors of fieldwork while still delivering accurate measurements.

In summary, the Fluke 2625A is a powerful data logger that combines versatility, accuracy, and reliability. Its user-friendly interface, advanced measurement technologies, and robust design make it an essential tool for professionals in various industries, from manufacturing and HVAC to research and development. Whether monitoring temperature changes in a laboratory or assessing voltage levels in an industrial setting, the Fluke 2625A stands out as a trusted solution for effective data logging and analysis.
Top Page Image Contents