XC2200 Derivatives
System Units (Vol. 1 of 2)
Interrupt and Trap Functions
User’s Manual
5-26
V2.1, 2008-08
ICU_X2K, V2.2
Note: If word data transfer is selected for a specific PEC channel (BWT = 0), the
respective source and destination pointers must both contain a valid word address
which points to an even byte boundary. Otherwise, the Illegal Word Access trap
will be invoked when this channel is used.
5.4.3
PEC Transfer Control
The PEC Transfer Count Field COUNT controls the behavior of the respective PEC
channel. The contents of bitfield COUNT select the action to be taken at the time the
request is activated. COUNT may allow a specified number of PEC transfers, unlimited
transfers, or no PEC service at all.
summarizes, how the COUNT field, the
interrupt requests flag IR, and the PEC channel action depend on the previous contents
of COUNT.
Table 5-7
PEC Data Pointer Register Addresses
Channel #
0
1
2
3
4
5
6
7
PECSEGx
EC80
H
EC82
H
EC84
H
EC86
H
EC88
H
EC8A
H
EC8C
H
EC8E
H
SRCPx
EC40
H
EC44
H
EC48
H
EC4C
H
EC50
H
EC54
H
EC58
H
EC5C
H
DSTPx
EC42
H
EC46
H
EC4A
H
EC4E
H
EC52
H
EC56
H
EC5A
H
EC5E
H
Table 5-8
Influence of Bitfield COUNT
Previous
COUNT
Modified
COUNT
IR after
Service
Action of PEC Channel and Comments
FF
H
FF
H
0
Move a Byte/Word
Continuous transfer mode, i.e. COUNT is not
modified
FE
H
… 02
H
FD
H
… 01
H
0
Move a Byte/Word and decrement COUNT
01
H
00
H
1
EOPINT = 0
(channel-specific interrupt)
Move a Byte/Word and leave request flag set,
which triggers another request
0
EOPINT = 1
(separate end-of-PEC interrupt)
Move a Byte/Word and clear request flag, set
the respective PEC subnode request flag CxIR
instead
1)
1) Setting a subnode request flag also sets flag EOPIR if the subnode request is enabled (CxIE = 1).
00
H
00
H
–
No PEC action!
Activate interrupt service routine rather than
PEC channel