During a trace, BitScope "marks" the data when a trigger event occurs.
The trigger is programmed to tell BitScope under what conditions the trigger event should occur.
Programming the trigger requires:
The third step is of course required only if an analog trigger is selected.
Three bits R7:0 and R7:2/1 are used to select the trigger source:
Bit Name Value Meaning 0 Trigger Source 0 Digital trigger source. 1 Analog trigger source. 2/1 Trigger Bit 7 0 DD7 : Digital Data Bus Bit 7. 1 Comparator : trigger match comparator signal. 2 Event 1 : (Pre-scaler output halved). 3 Event 2 : (ADC input halved).
When the Trigger Source is digital, the trigger is calculated using the 8 logic analyzer channels directly. When it is analog, the trigger is calculated using the 8 bit data from the A/D convertor.
Trigger Bit 7 must be set to Comparator for the selected Trigger Source to be used. The other choices are used for period measurement and other specialized functions which are described elsewhere.
The trigger is expressed as an 8 bit ternary number which is compared with the 8 logic analyzer channels or the 8 bit digitized analog signal. These bits express whether the trigger is to occur on a HIGH (1), LOW (0) or DON'T CARE (X) condition for each bit.
For example, a trigger on bits 0, 3, and 5 HIGH and bits 2 and 4 LOW with DON'T CARE for the rest is expressed as:
Trigger Condition = XX1010X1
The two trigger logic registers programmed together define this trigger condition:
R5 Trigger Logic Byte Logic values to match for trigger. R6 Trigger Mask Byte Don't care logic values for trigger.
The example trigger condition above could be programmed as:
R5 <- 00101001 R6 <- 11000010
where a HIGH (1) values in the Trigger Mask register R6 mean DON'T CARE regardless of the values in the corresponding bits in the Trigger Logic register R5.
When triggering on analog signals in any trace mode other than zero, the trigger registers are augmented with bits 4 and 5 of the Option Byte R7:
Bit Name Value Meaning 5 Trigger Type 0 Trigger operation is Level Sensitive. 1 Trigger operation is Edge Sensitive. 4 Edge Direction 0 Trigger asserted on FALSE -> TRUE 1 Trigger asserted on TRUE -> FALSE
To implement triggering on an analog signal zero crossing the trigger logic registers should be programmed as:
R5 <- 00000000 R6 <- 01111111
and R7:5 asserted for edge trigger operation. The value of R7:4 then determines whether the trigger occurs as the signal moves from negative to positive or vice versa.
By programming different values for R5 and R6 analog signal levels other than zero may be programmed. It is even possible to program multiple signal level bands for the analog trigger using DON'T CARE logic. Note that in trace mode zero, edge triggers do not apply and the values of these control bits are ignored.