RoboteQ AX2550/2850 user manual Counter Read Data Format, Speed 1, Time Base 1, Encoder Threshold

Counter Read Data Format

Speed 1 and 2

These registers contain a signed 8-bit value (-127 to +127) that represents the motor speed relative to a maximum speed, which in turn depends on the number of encoder counts and time base settings as described in “Using the Encoder to Measure Speed” on page 139.

Time Base 1 and 2

These registers contain the timing information for measuring the speed. See “Using the Encoder Module to Measure Distance” on page 138 for a detailed description.

Encoder Threshold

This register contains a value that is used to detect a logic level 1 vs. a 0 at any of the 4 encoder input lines. Voltage threshold is computed as follows:

Voltage Threshold = 5V * Register Value / 255

See “Voltage Levels, Thresholds and Limit Switches” on page 136 for a detailed descrip- tion.

Counter Read Data Format

When receiving a counter read query, the encoder module will output the value of its 32-bit counter. If all 32-bit are sent, this would require 8 ASCII digits to represent the value.

A 32-bit counter can store over 2 billion counts in each direction. Practically, it will be rare that counts will be that large and therefore only a partial number of the counter’s bits will be significant at any given time.

In order to create a more efficient data stream on the controller’s serial port, a simple com- pression technique is implemented. The scheme eliminates all of the counter’s most signif- icant bits if they are at 0 (for a positive count number) or F (for a negative count number).

For example, if the counter value is Hex 00000015, the value 15 will be returned after a counter query.

For negative numbers, a count value of -5 (which is FFFFFFFB in hex), the response to the query will be B.

To distinguish between positive and negative numbers, the Encoder module will insert a 0 ahead of any number string starting with a digit value higher than 7 (i.e. 8 to F) to signify that the number is positive. For negative numbers, the Encoder module will insert an F ahead of any number string starting with a digit value lower than 8 (i.e. 0 to 7). The table below shows examples of this scheme as applied to various counter values

TABLE 26. Example counter values and RS232 output using reduction scheme

Decimal	32-bit Hex	Controller Output
+5	00000005	5
+250	000000FA	0FA
-6	FFFFFFFA	A

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