ST10R272L STMicroelectronics, ST10R272L Datasheet - Page 21

• Manufacturer Part Number: ST10R272L
• Description: 16-BIT Romless MCU WITH MAC UNIT
• Manufacturer: STMicroelectronics

Specifications of ST10R272L

• Cpu Frequency: 0 to 50 MHz
• Power: 3.3 Volt +/-0.3V

of repetition that remains to complete the sequence. If the Repeat Unit is used in the interrupt
routine, MRW must be saved by the user and restored before the end of the interrupt routine.
Note
MAC interrupt
The MAC can generate an interrupt according to the value of the status flags C (carry), SV
(overflow), E (extension) or SL (limit) of the MSW. The MAC interrupt is globally enabled when
the MIE flag in MCW is set. When it is enabled the flags C, SV, E or SL can triggered a MAC
interrupt when they are set provided that the corresponding mask flag CM, VM, EM or LM in
MCW is also set. A MAC interrupt request set the MIR flag in MSW, this flag must be reset by
the user during the interrupt routine otherwise the interrupt processing restarts when
returning from the interrupt routine.
The MAC interrupt is implemented as a Class B hardware trap (trap number Ah - trap priority
I). The associated Trap Flag in the TFR register is MACTRP, bit #6 of the TFR (Remember
that this flag must also be reset by the user in the case of an MAC interrupt request).
As the MAC status flags are updated (or eventually written by software) during the Execute
stage of the pipeline, the response time of a MAC interrupt request is 3 instruction cycles (see
Figure 3). It is the number of instruction cycles required between the time the request is sent
and the time the first instruction located at the interrupt vector location enters the pipeline.
Note that the IP value stacked after a MAC interrupt does not point to the instruction that
triggers the interrupt.
FETCH
DECODE
EXECUTE
WRITEBACK
The Repeat Count should be used with caution. In this case MR should be written as
0. In general MR should not be set by the user otherwise correct instruction
processing can not be guaranteed.
Figure 7 Pipeline diagram for MAC interrupt response time
N
N-1
N-2
N-3
N+1
N
N-1
N-2
ST10R272L - MULTIPLY-ACCUMULATE UNIT (MAC)
N+2
N+1
N
N-1
MAC Interrupt Request
N+3
N+2
N+1
N
Response Time
N+4
TRAP (1)
N+2
N+1
I1
TRAP (2)
TRAP (1)
N+2
I2
I1
TRAP (2)
TRAP (1)
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