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A-2 Digital I/O

General Info

Below you can find information regarding the T7's Digital Input/Output lines.

Table A2-1. IO Information

Parameter Conditions Min Typical Max Units
Low Level Input Voltage   -0.3   0.5 Volts
High Level Input Voltage   2.64   5.8 Volts
Hysteresis Voltage (1)          
---Low to High Transition       1.15 Volts
---High to Low Transition   0.90     Volts
Maximum Input Voltage (2) FIO -10   10 Volts
  EIO/CIO/MIO -6   6 Volts
Output Low Voltage (3, 4) No Load   0.01   Volts
---FIO Sinking 1 mA   0.55   Volts
---EIO/CIO Sinking 1 mA   0.15   Volts
---EIO/CIO Sinking 5 mA   0.75   Volts
Output High Voltage (3, 4) No Load   3.3   Volts
---FIO Sourcing 1 mA   2.75   Volts
---EIO/CIO Sourcing 1 mA   3.15   Volts
---EIO/CIO Sourcing 5 mA   2.6   Volts
Short Circuit Current (3, 4) FIO   6.3   mA
  EIO/CIO/MIO   22.9   mA
Output Impedance (3, 4) FIO   550   Ω
  EIO/CIO/MIO   180   Ω
           
(1) The "Low Level" and "High Level" input voltage specify input voltage ranges guaranteed to produce the correct logic state at any digital input. The "Hysteresis Voltage" represents the voltage where a logic transition will actually occur. Input hysteresis will result in different transition voltages, depending on transition from HIGH to LOW or LOW to HIGH logic states. The overall hysteresis band is ~0.25 Volts.     
(2) Maximum voltage to avoid damage to the device. Protection works whether the device is powered or not, but continuous voltages over 5.8 volts or less than -0.3 volts are not recommend when the T7 is unpowered, as the voltage will attempt to supply operating power to the T7 possibly causing poor start-up behavior.     
(3) These specifications provide the answer to the question. "How much current can the digital I/O sink or source?". For instance, if EIO0 is configured as output-high and shorted to ground, the current sourced by EIO0 is configured as output-high and shorted to ground, the current sourced by EIO0 into ground will be about 16 mA (3.3/180). If connected to a load that draws 5 mA, EIO0 can provide that current but the voltage will droop to about 2.4 volts instead of the nominal 3.3 volts. If connected to a 180 ohm load to ground, the resulting voltage and current will be about 1.65 volts @ 9 mA.     
(4) It is recommended to use the EIO/CIO digital I/O lines for UART, SPI, I²C, 1-Wire, and other digital communication protocols.     

Extended Features

Below you can find information regarding the T7's DIO EF.

Table A2-2. DIO extended features information

Extended Features Conditions Min Typical Max Units
Frequency Output (1)   0.02   5 M Hz
           
Counter Input Frequency (2)       5 MHz
Minimum High & Low Time (2)       50 ns
"Interrupt" Total Edge Rate (3)(4) No Stream     70k edges/s
  While Streaming @ 50 kHz     20k edges/s
           
(1) Frequencies up to 40MHz are possible, but they are heavily filtered.     
(2) Hardware counters. 0 to 3.3 volt square wave.     
(3) This is for the "Interrupt" modes. To Avoid missing edges, keep the total number of applicable edges on all applicable timers below this limit.     
(4) Excessive processor loading could reduce these limits further.     



Serial Communication

Below you can find information regarding the T7's Serial Communication abilities. Please keep in mind our devices use 3.3V logic levels and provide 5V output along the VS screw terminal. Some ICs require the same logic level as provided to the chip's VCC line so extra steps may be required to integrate specific sensors.

Table A2-3. Serial communication information

Serial Communication Conditions Min Max Units
SPI Characteristics        
Clock Frequencies   0.08718 870 kHz
         
I2C Characteristics        
Clock Frequencies   9.3 472 kHz

2 comments

If I want to scan DIO[0-15] in stream mode, what maximum effective scan rate i can get? Actually i am confused whether maximum scan rate will be 100KS/2 or 100KS/16. My understanding is that maximum scan rate is 100KS/NumberOfAddresses. Since i am scanning two ports, address count for two ports will be 16 (bit address) or 2 (byte address).

If you look at the modbus map and set Tags=DIO, you will see the bit registers FIO# & EIO#, the single-port registers FIO_STATE & EIO_STATE, and the double-port register FIO_EIO_STATE, but what you don't see is whether these are streamable or not.  If you look at Section 3.2 of the T7 Datasheet you can see that all the port registers are listed but not the bit registers, and this is confirmed by looking at ljm_constants.json where we see "streamable":true for the port registers but not the bit registers.  So you can do 100k / 2 single-port addresses to scan 16 digital inputs every 20 us, or you can do 100k / 1 double-port address to scan 16 digital inputs every 10 us. In fact, using Ethernet you will probably be able to get closer to 120k streaming.