ST10R272L - INTERRUPT AND TRAP FUNCTIONS
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Continuous transfers are selected by the value ‘FFh’ in bit field COUNT. COUNT is not
modified and the PEC channel services any request until it is disabled again.
When COUNT is decremented from 01h to 00h after a transfer, the request flag is not
cleared, which generates another request from the same source. When COUNT already
contains the value 00h, the PEC channel remains idle and the associated interrupt service
routine is activated instead. Therefore, you can choose whether level 15 or 14 requests are
to be serviced by the PEC or by the interrupt service routine.
Note
PEC transfers are only executed if their priority level is higher than the CPU level,
i.e. only PEC channels 7...4 are processed while the CPU executes on level 14.
All interrupt request sources that are enabled and programmed for PEC service
should use different channels. Otherwise only one transfer will be performed for all
simultaneous requests. When COUNT is decremented to 00h, and the CPU is to be
interrupted, an incorrect interrupt vector will be generated.
The source and destination pointers specify the locations between which the data is to be
moved. A pair of pointers (SRCPx and DSTPx) is associated with each of the 8 PEC
channels. These pointers do not reside in specific SFRs, but are mapped into the internal
RAM of the ST10R272L just below the bit-addressable area (see figure below).
PEC data transfers do not use the data page pointers DPP3...DPP0. The PEC source and
destination pointers are used as 16-bit intra-segment addresses within segment 0, so that
data can be transferred between any two locations in the first four data pages 3...0.
The pointer locations for inactive PEC channels may be used for general data storage. Only
the required pointers occupy RAM locations.
If word data-transfer is selected for a specific PEC channel (i.e. BWT=’0’), the respective
source and destination pointers must both contain a valid word address which points to an
even byte boundary. Otherwise an Illegal Word Access trap will be invoked when this
channel is used.
01h 00h ‘1’
Move a Byte / Word
Leave request flag set, which triggers another request
00h 00h ‘1’
No
action!
Activate interrupt service routine rather than PEC
channel.
1.
After PEC service
COUNT
COUNT
1
IR after PEC
service
Action of PEC Channel and Comments
Table 16 Dependency on COUNT of the count field, IR and PEC channel
