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TC1796
System Units (Vol. 1 of 2)
System Control Unit
User’s Manual
5-11
V2.0, 2007-07
SCU, V2.0
The ETL of the input channel analyzes the synchronized output signal INx of the ERS by
an edge-detection logic. This edge-detection block generates a pulse (one clock cycle
long) when a signal transition is detected. The selection which signal transition (edge)
should generate a pulse (event) is done by two control bits, one for the rising edge
(EICRn.RENx) and one for the falling edge (EICRn.FENx). Therefore, only a rising or
falling edge, or both edges of the input signal can be detected. When a selected signal
transition is detected, the external interrupt flag EIFRn.INTFx becomes always set by
hardware, even it is has been set previously. The interrupt flag EIFRn.INTFx is available
as output signal INTFx of the ETL.
The hardware reset condition for EIFRn.INTFx can be controlled in two different ways.
These two modes are selected by bit EIFRn.LDENx.
•
EIFRn.LDENx = 0:
Flag EIFRn.INTFx is used as a sticky bit, indicating that the selected signal transition
has been detected by the edge-detection logic at least once. In this mode, bit
EIFRn.INTFx can be cleared only by software.
•
EIFRn.LDENx = 1:
In this mode, flag EIFRn.INTFx becomes cleared by hardware if an edge is detected
at the INx signal, that has not been selected. This means, EIFRn.INTFx is cleared by
hardware at a INx rising edge when EICRn.FENx = 1 and EIFRn.INTFx is cleared by
hardware at a INx falling edge when EICRn.RENx = 1. If both bits, EICRn.FENx and
EICRn.RENx, are set, flag EIFRn.INTFx becomes never cleared by hardware. In this
case, flag EIFRn.INTFx can be only cleared by software.
Flag EIFRn.INTFx can be set or cleared by software using the bits FSx or FCx in the flag
modification register FMR. Writing to FMR with bit FMR.FSx set sets flag EIFRn.INTFx.
Writing to FMR with bit FMR.FCx set clears flag EIFRn.INTFx. If both bits are set for one
input channel x, a set operation of the flag will be executed.
Each output pulse of the edge-detection block that sets the EIFRn.INTFx flag by
hardware can be routed also to one of the INTx[3:0] outputs of the ETL unit. The external
interrupt enable bit EICRn.EIENx = 1 enables the interrupt output pulse at the INTx[3:0]
outputs. Bit field EICRn.INPx controls which of the INTx[3:0] outputs is selected for the
output pulse.