ST10R272L - INTERRUPT AND TRAP FUNCTIONS
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interrupt system of the ST10R272L and the arbitration mechanism for the external bus
interface.
Note
Pipeline effects must be considered when enabling/disabling interrupt requests by
modifying the PSW register (ref to “Processor status word PSW” on page 50).
PSW (FF10h / 88h)
SFR
Reset Value: 0000h
CPU Priority ILVL defines the CPU priority level. It shows the priority level of the routine that
is currently being executed. On the entry into an interrupt service routine, this bit field is
updated with the priority level of the request that is being serviced. The PSW is saved on the
system stack. The CPU level determines the minimum interrupt priority level that will be
serviced. Any request on the same or a lower level will not be acknowledged.
The current CPU priority level may be changed by software to control which interrupt request
sources will be acknowledged.
PEC transfers do not really interrupt the CPU, but rather ‘steal’ a single cycle, so PEC
services do not influence the ILVL field in the PSW.
Hardware Traps switch the CPU level to maximum priority (i.e. 15), so no interrupt or PEC
requests are acknowledged while an exception trap service routine is being executed.
Bit
Function
N, C, V, Z, E,
MULIP, USR0
CPU status flags (see “Saving the status during interrupt service” on page 96)
Define the current status of the CPU (ALU, multiplication unit).
HLDEN
HOLD Enable (Enables External Bus Arbitration)
0: Bus arbitration disabled, P6.7...P6.5 may be used for general purpose IO
1: Bus arbitration enabled, P6.7...P6.5 serve as BREQ, HLDA, HOLD, resp.
ILVL
CPU Priority Level
Defines the current priority level for the CPU
Fh: Highest priority level
0h: Lowest priority level
IEN
Interrupt Enable Control Bit (globally enables/disables interrupt requests)
‘0’: Interrupt requests are disabled
‘1’: Interrupt requests are enabled
HLD
EN
-
MUL
IP
USR0
N
Z
C
V
E
5
4
3
2
1
0
11
10
9
8
7
6
15
14
13
12
rw
rw
rw
rw
-
rw
rw
rw
-
rw
-
rw
IEN
-
-
ILVL
rw