Measurement-computing USB-4301 Manuale Utente Scaricare il pdf (Pagina 22)

USB-4301 User's Guide Specifications

Parameter

Conditions

12 MHz crystal oscillator accuracy

±50 ppm

High pulse width (clock input)

25 ns min

Low pulse width (clock input)

25 ns min

Gate width

70 ns min

Input low voltage

-0.5 V min, 0.8V max

Input high voltage

2.0 V min, USB +5V power max

Output low voltage @ IIl=4 mA

0.4 V max

Output high voltage @ IIH= 4 mA

2.4 V min

Digital input / output

Table 2. Digital I/O specifications

Digital type

Discrete, 5V/TTL compatible

Output: 74ACT373

Input: 74ACT373

Number of I/O

8 input, 8 output

Configuration

1 bank of 8 as output, 1 bank of 8 as input

Input high voltage

2.0 V min,5.5 V absolute max

Input low voltage

0.8 V max, –0.5 V absolute min

Output high voltage

3.3 volts min @ -24 mA (Vcc = 4.5 V)

Output low voltage

0.8 volts max @ 10 mA

Data transfer

Programmed I/O

Power-up / reset state

Digital outputs reset to TTL low

Digital I/O transfer rate

(system paced)

System dependent, 33 to 1000 port reads/writes or single bit reads/writes per

second.

Pull-up/pull-down configuration

User configurable for pull-up/-down through 47 kΩ resistor (Note 1).

All pins floating (default)

Note 1: Pull-up and pull-down configurations are available using the DI CTL terminal block pin 19. The

pull-down configuration requires the DI CTL pin (pin 19) to be connected to a GND pin (pin 10,

20, 38, or 48). For a pull-up configuration, the DI CTL pin should be connected to a +5V

terminal pin (pin 8 or 18).

Interrupt Input

Table 3. Interrupt specifications

Implementation

Interrupts the microcontroller operation on the device to execute one or more of

several firmware routines.

Interrupt characteristics

Rising edge (default) or falling edge triggered, user selectable

Firmware routines

Any or all of the following can be activated by the user:

 Generate USB event notification

 Latch digital inputs (Reading digital inputs returns most recently latched

value.)

 Latch digital outputs (Most recently written digital output value is latched.)

 Save counts on any/all of counters 1-5.

Event latency to PC

1-33 ms (4 ms typical)

Maximum event notification rate

33-1000 Hz (system dependent) (Note 2)

Interrupt latency for latch operations

100 µs maximum (80 µs typical)

Note 2: The interrupt rate, when transferring information to the PC (event notification), is limited by the

USB to a theoretical limit of 1kHz. Some systems may not be able to achieve this maximum rate

due to differences in USB controller implementation, traffic on the USB, or operating system

activity.

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