13.2.4 Pulse Out [T-Series Datasheet] | LabJack
 
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13.2.4 Pulse Out [T-Series Datasheet]

Overview

 

T4 Capable DIO: DIO6, DIO7 (aka FIO6, FIO7)

 

T7 Capable DIO: DIO0, DIO2, DIO3, DIO4, DIO5 (aka FIO0, FIO2, FIO3, FIO4, FIO5)

Requires Clock Source: Yes

Index: 2

Streamable: No

Operation

Pulse output will generate a specified number of pulses. The high time and the low time are specified relative to the clock source the same way as PWM with Phase.

Clock#Frequency = CoreFrequency / DIO_EF_CLOCK#_DIVISOR    // typically 80M/Divisor
PulseOutFrequency = Clock#Frequency / DIO_EF_CLOCK#_ROLL_VALUE
DutyCycle% = 100 * (DIO#_EF_CONFIG_A - DIO#_EF_CONFIG_B) / DIO_EF_CLOCK#_ROLL_VALUE    // if A > B

For the common case of CoreFrequency = 80 MHz and CONFIG_B fixed at 0, we can rewrite these as:

PulseOutFrequency = 80M / (DIO_EF_CLOCK#_DIVISOR * DIO_EF_CLOCK#_ROLL_VALUE)
DutyCycle% = 100 * DIO#_EF_CONFIG_A / DIO_EF_CLOCK#_ROLL_VALUE

... and thus for 50% duty cycle simply set:

DIO#_EF_CONFIG_A = DIO_EF_CLOCK#_ROLL_VALUE / 2

CoreFrequency is always 80 MHz at this time, but in the future some low-power operational modes might result in different core frequencies.  The valid values for DIO_EF_CLOCK#_DIVISOR are 1, 2, 4, 8, 16, 32, 64, or 256, and a value of 0 (default) equates to a divisor of 1.  For more details about Clock#Frequency and DIO_EF_CLOCK#_DIVISOR, see the DIO-EF Clock Source section.

The clock roll value can take up to one pulse out period to update and this does not block subsequent commands from being processed. It is possible to finish updating DIO_EF_CONFIG_A or DIO_EF_CONFIG_B to a value greater than the non-updated clock roll value (which is invalid) but less than the updated clock roll value (which is valid) and throw the error 2565: EF_VALUE_GREATER_THAN_PERIOD.
 
Potential fixes:
  • disable and re-enable the clock line before updating the clock roll value and  line transition values.
  • Delay for greater than one "non-updated" period between updating the clock roll value and updating the line transition values.

Configure

DIO#:  First set the DIO line low (DIO#=0). The line must start low for proper pulse generation.
DIO#_EF_ENABLE: 0 = Disable, 1 = Enable
DIO#_EF_INDEX: 2
DIO#_EF_OPTIONS: Bits 0-2 specify which clock source to use ... 000 for Clock0, 001 for Clock1, and 010 for Clock2. All other bits are reserved and should be set to 0.
DIO#_EF_CONFIG_A: When the specified, clock source's count matches this value the line will transition from high to low.
DIO#_EF_CONFIG_B: When the specified, clock source's count matches this value the line will transition from low to high.
DIO#_EF_CONFIG_C: The number of pulses to generate.
DIO#_EF_CONFIG_D: Not used.

Update

DIO#_EF_CONFIG_A: Sets a new high to low transition point. Will take effect when writing CONFIG_C.
DIO#_EF_CONFIG_B: Sets a new low to high transition point. Will take effect when writing CONFIG_C.
DIO#_EF_CONFIG_C: Writing to this value will start a new pulse sequence. If a sequence is already in progress it will be aborted. Numbers previously written to CONFIG_A or CONFIG_B will take effect when CONFIG_C is written.

Read

Results are read from the following registers.

DIO#_EF_READ_A: The number of pulses that have been completed.
DIO#_EF_READ_B: The target number of pulses.

Reset

DIO#_EF_READ_A_AND_RESET: Reads number of pulses that have been completed, then restarts the pulse sequence.

Example

First configure a clock source to drive the pulse generator. Assuming the core frequency is 80 MHz, writing the following registers will produce a 1 kHz pulse frequency.

DIO_EF_CLOCK0_DIVISOR = 8
DIO_EF_CLOCK0_ROLL_VALUE = 10000
DIO_EF_CLOCK0_ENABLE = 1

Thus the clock frequency is:

Clock0Frequency = 80 MHz / 8 = 10 MHz

and PWM frequency is:

PWMFrequency = 10 MHz / 10000 = 1 kHz

Now that we have a clock to work with, we can configure our pulse.

DIO0_EF_ENABLE = 0
DIO0 = 0                  // set DIO0 to output-low
DIO0_EF_INDEX = 2         // pulse out type index
DIO0_EF_CONFIG_A = 2000   // high to low count
DIO0_EF_CONFIG_B = 0      // low to high count
DIO0_EF_CONFIG_C = 5000   // number of pulses
DIO0_EF_ENABLE = 1

Thus, the duty cycle is:

duty cycle = 100 * (2000 - 0) / 10000 = 20%

The LabJack will now output 5000 pulses over 5 seconds at 20% duty cycle.