Sign in

Explanation of Supported IO voltages, Voltage Thresholds, and Over-Voltage Protection

Follow

This article explains the digital input voltage standards for all of the Saleae devices.

There are two important specifications to keep in mind when determining what signals can be recorded with the Saleae products, and what signals could potentially damage the device.

The first is the supported IO thresholds. These define the voltage thresholds that determine what is recorded as a digital 0 and a digital 1.

Second is the over-voltage protection. This determines the maximum input voltage that can be applied without risking damage to the device.

These specifications are also listed on the device information tile on the Saleae home page. https://www.saleae.com/#DatasheetTile

For all Saleae products, all inputs share the same IO threshold. For products with selectable thresholds, there is no way to assign different IO thresholds to different pins at the same time - all pins share the same threshold setting.

Logic 4

Logic 4 has a simple, fixed input voltage threshold.

Voltage input low: 0.8 volts

Voltage input high: 2.0 volts

Over-voltage protection provides safety to +/- 25V

Notes:

  • Over-voltage protection is sufficient to use this product safely with RS-232, RS-485, 12V TTL, and other larger swing signals inside of the +/- 25 V range. No adapter or additional protection is required.
  • Because of the voltage input high threshold of 2.0 volts, this device cannot be used with 1.8V or 1.2V logic. It also cannot be directly connected to 3.3V CAN signals. Please see our article about - recording CAN for more details.
  • Recommended IO standards: 5.0V, 3.3V, 2.5V

The New Logic 8

The new Logic 8 also has a fixed input voltage threshold.

Voltage input low: 0.6 volts

Voltage input high: 1.2 volts

Over-voltage protection provides safety to +/- 25V

Notes:

  • Over-voltage protection provides the same benefits as the other new devices, as listed in the notes for Logic 4.
  • The 1.2V input voltage high spec allows Logic 8 to be used directly with the CAN low channel of 3.3V CAN
  • Recommended IO standards: 5.0V, 3.3V, 2.5V, 1.8V

Logic Pro 8 and Logic Pro 16

The Logic Pro devices have three selectable threshold voltage options. Also, the inputs are implemented with comparators, instead of standard CMOS buffers like Logic 4 and the new Logic 8. This makes the input low and input high voltages very close to each other. The exact behavior of these comparators is not defined here.

1.2V Voltage Option

  • Voltage threshold: 0.6V

1.8V Voltage Option

  • Voltage threshold: 0.9V

+3.3V Voltage Option

  • Voltage threshold: 1.65V
  • Use this option for all IO standards 3.3 volts or above.

Over-voltage protection provides safety to +/- 25V

Notes:

  • Over-voltage protection provides the same benefits as the other new devices, as listed in the notes for Logic 4.
  • Recommended IO standards: 5.0V, 3.3V, 2.5V, 1.8V, 1.2V
  • The precise threshold voltage is not calibrated, and may vary as much as +/- 15%. This is more than accurate enough to record standard IO families.

The First Generation Logic

The original Logic also has a fixed input voltage threshold.

Voltage input low: 0.8 volts

Voltage input high: 2.0 volts

Over-voltage protection provides safety to +/- 15V

Note: Over-voltage protection not meant for continuous operation outside of -0.5V to 5.25V. This makes the device unsuitable for safe direct recording of RS-232 and similar standards.

The original logic is the only Saleae device to have internally pulled up inputs. All other Saleae devices had an internal resistance to ground. The original Logic's inputs float at about 2.4 volts, with over 100 K ohms of pull-up resistance, producing a very small pull up effect.

The First Generation Logic16

The original Logic16 had two selectable threshold settings.

Lower threshold setting (for use with IO families in the range of 1.8V to 3.6V)

  • Voltage input low: 0.7V
  • Voltage input high: 1.5V Upper threshold settings (for use with 5.0V logic or larger signals)

  • Voltage input low: 1.4V

  • Voltage input high: 3.6V Over voltage protection provides safety to +/- 50V

Note: Over-voltage protection not meant for continuous operation outside of -0.9V to 6V. This makes the device unsuitable for safe direct recording of RS-232 and similar standards.

Input threshold variation

There might be some small variation in the precise threshold voltage channel to channel. This is most notable in the Saleae Logic Pro devices, because comparitors with low hysteresis are used.

Tags: What is the high logic voltage level on Saleae Logic? What is the low logic voltage level on Saleae Logic?


trello ID: 55f32deb2d14d47eaaac7bf9
Have more questions? Submit a request

Comments

Powered by Zendesk