4.4 CONTROLLING THE TRIGGERS
The carrier implements flexible trigger control capabilities providing the user with many options for using triggers. Each M-module can support two trigger lines (labeled A & B) which can be mapped to one of two external trigger lines (one input and one output) available on the carrier or to the trigger lines of the adjacent M-module.
The carrier’s external trigger lines can be accessed at the 9-pin DSUB connector on the back panel of the EM405D. Refer to Appendix A for pin-out details of the 9-pin DSUB connector. The input trigger line has a software configurable threshold and input impedance. The input threshold is configurable using the TLVL bit in the Reset & Trigger Control register and can be set to either +1.4 volts or +2.5 volts. The input impedance is configurable using the TIMP bit in the Reset & Trigger Control register and can be set to either high impedance (>100KΩ) or 50Ω. The output trigger line has a set output impedance of 50Ω and a set output drive level of +5V (typical) into a high impedance load.
Each M-module trigger line can be configured to be either an input or an output and can be mapped to either the external trigger lines or to one of the trigger lines on the other M-module. Each trigger line contains two bit fields in the Reset & Trigger Control register. The xTzD bit controls the trigger direction and the xTzM controls the trigger mapping, where x specifies the module and z specifies the trigger (for example ATBM is module A trigger B). If the xTzM bit field is set to map the trigger line to the external trigger, the trigger is connected to either the external input or the external output depending on the value of the xTzD bit. If the xTzM bit field is set to map the trigger line to another M-module trigger line, then the two triggers must be configured to be opposite directions. Also the second M-module trigger line must be mapped to the first M-module trigger line. For example, if module A trigger B is to be outputted to module B trigger A then the corresponding bit fields must be set as follows:
ATBD = output
ATBM = to/from Module B Trigger A
BTAD = input
BTAM = to/from Module A Trigger B
The following values would be invalid:
ATBD = output
ATBM = to/from Module B Trigger A
BTAD = output
BTAM = to/from Module A Trigger B
or
ATBD = output
ATBM = to/from Module B Trigger A
BTAD = input
BTAM = to/from external trigger
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