MPC555
/
MPC556
MODULAR INPUT/OUTPUT SUBSYSTEM (MIOS1)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
15-12
cording to this level, the ICS sets the correct IRQ[7:0] lines with the correct ILBS[1:0]
time multiplex lines on the peripheral bus. The CPU is then informed as to which of the
thirty-two interrupt levels is requested.
Based on the interrupt level requested, the software must determine which submodule
requested the interrupt. The software may use a find-first-one type of instruction to de-
termine, in the concerned MIRSM, which of the bits is set. The CPU can then serve
the requested interrupt.
15.9 MIOS Counter Prescaler Submodule (MCPSM)
The MIOS counter prescaler submodule (MCPSM) divides the MIOS1 clock (F
SYS
) to
generate the counter clock. It is designed to provide all the submodules with the same
division of the main MIOS1 clock (division of F
SYS
). It uses a 4-bit modulus counter.
The clock signal is prescaled by loading the value of the clock prescaler register into
the prescaler counter every time it overflows. This allows all prescaling factors be-
tween two and 16. Counting is enabled by asserting the PREN bit in the control regis-
ter. The counter can be stopped at any time by negating this bit, thereby stopping all
submodules using the output of the MCPSM (counter clock).
Figure 15-3 MCPSM Block Diagram
15.9.1 MIOS Counter Prescaler Submodule (MCPSM) Registers
is the address map for the MCPSM submodule.
f
SYS
Prescaler
PREN
CP2
CP1
CP0
Decrementer
Clock
Register
Load
CP3
Enable
MCPSMSCR
4-bit
= 1?
Dec.
Counter Clock
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Freescale Semiconductor, Inc.
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