HTU
DCP[0]
DCP[1]
DCP[2]
DCP[3]
DCP[4]
DCP[5]
DCP[6]
DCP[7]
DMA
DMAREQ[20]
DMAREQ[21]
DMAREQ[24]
DMAREQ[25]
N2HET
DMAREQ[0]
HTUREQ[0]
DMAREQ[1]
HTUREQ[1]
DMAREQ[2]
HTUREQ[2]
DMAREQ[3]
HTUREQ[3]
DMAREQ[4]
HTUREQ[4]
DMAREQ[5]
HTUREQ[5]
DMAREQ[6]
HTUREQ[6]
DMAREQ[7]
HTUREQ[7]
N2HET Functional Description
990
SPNU563A – March 2018
Copyright © 2018, Texas Instruments Incorporated
High-End Timer (N2HET) Module
23.2.9 N2HET Requests to DMA and HTU
As described in
, the majority of the N2HET instructions are able to generate a transfer
request to the High-End Timer Transfer Unit (HTU) and/or to the DMA module when an instruction-specific
condition is true. One N2HET instruction can select one of 8 request lines by programming the “reqnum”
parameter. The “request” field in an instruction is used to enable, disable, or to generate a quiet request
(see
) on the selected request line. Quiet requests can be used by the HTU, but not by the
DMA. For quiet request, refer to the
High-End Timer Transfer Unit (HTU) Module
chapter (see
The configuration of the N2HET Request Destination Select Register (HETREQDS) bits determines if a
request line triggers an HTU-DCP, a DMA channel or both. This means the register bits will determine
whether an N2HET instruction triggers DMAREQ[x], HTUREQ[x] or both signals (shown in
).
The request line number x corresponds to the “reqnum” parameter used in the instruction.
Figure 23-29. Request Line Assignment Example
23.3 Angle Functions
Engine management systems require an angle-referenced time base to synchronize signals to the engine
toothed wheel. The N2HET has a method to provide such a time base for low-end engine systems. The
reference is created by the N2HET using three dedicated instructions with fractional angle steps equal to
/8, /16, /32, /64.
23.3.1 Software Angle Generator
The N2HET provides three specialized count instructions to generate an angle referenced time base
synchronized to an external reference signal (the toothed wheel signal) that defines angular reference
points.
The time base is used to generate fractional angle steps between the reference points. The step width K
(= 8, 16, 32, or 64) programmed by the user defines the angle accuracy of the time base. These fractional
steps are then accumulated in an angle counter to form the absolute angle value.
The first counter, APCNT, incremented on each loop resolution clock measures the periods P(n) of the
external signal. The second counter SCNT counts by step K up to the previous period value P(n-1),
measured by APCNT, and then recycles. The resulting period of SCNT is the fraction P(n-1) / K. The third
counter ACNT accumulates the fractions generated by SCNT.
illustrates the basic operation of APCNT, SCNT, and ACNT.
A N2HET timer program can only have one angle generator.
