TS-7180 Quadrature
Quadrature Counters
The TS-7180 provides three independent quadrature counters. The associated inputs are shown in the table below.
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Each of the quadrature counters (which are in the FPGA) is 16-bits wide, and are accessed via i2c. The addresses are shown below.
| Quad # | MSB | LSB | MSB Alias |
|---|---|---|---|
| Quad0 | 96 | 97 | 98 |
| Quad1 | 99 | 100 | 101 |
| Quad2 | 102 | 103 | 104 |
For example, to read the MSB for Quad1:
tshwctl -r -a 99
The MSB aliases are used to detect 16-bit rollover. If the first reading of the MSB is not equal to the second, overflow/underflow was detected during the read.
Edge-Counters, Period-counters
For each input pin, there is an edge-counter, and a period-counter. The former counts the positive edges on an input pin, while the latter may be used to measure the elapsed time between N positive-edges.
Edge-counters are 16-bits wide, and their addresses are shown in the table below.
| Input | MSB | LSB | MSB Alias |
|---|---|---|---|
| DIG_IN_1 | 105 | 106 | 107 |
| DIG_IN_2 | 108 | 109 | 110 |
| DIG_IN_3 | 111 | 112 | 113 |
| DIG_IN_4 | 114 | 115 | 116 |
| DIO_6_IN | 117 | 118 | 119 |
| DIO_7_IN | 120 | 121 | 122 |
Period counters are 32-bits wide, and their addresses are shown in the table below.
| Input | Byte 3 | Byte 2 | Byte 1 | Byte 0 |
|---|---|---|---|---|
| DIG_IN_1 | 131 | 132 | 133 | 134 |
| DIG_IN_2 | 135 | 136 | 137 | 138 |
| DIG_IN_3 | 139 | 140 | 141 | 142 |
| DIG_IN_4 | 143 | 144 | 145 | 146 |
| DIO_6_IN | 147 | 148 | 149 | 150 |
| DIO_7_IN | 151 | 152 | 153 | 154 |
To use the period counters, it is first necessary to write N (for the number of edges to count) to address 155. This may be done like so:
tshwctl -a 155 -w N
As soon as address 155 is written, counting begins, clocked at 63MHz. After N edges have been detected, the period registers may be read. The frequency of the input may be calculated from the period, as shown here:
frequency = (N * 63000000) / period
Technologic Systems has provided a simple test program for accessing and displaying the values from the quadrature and edge-counters. Download the source tarball here: File:Test-edges.tar.gz