XC2200 Derivatives
System Units (Vol. 1 of 2)
Architectural Overview
User’s Manual
2-17
V2.1, 2008-08
ArchitectureX22, V1.1
instructions (BFLDL and BFLDH) to write to any number of bits in either byte of an
SFR without disturbing the non-addressed byte and the unselected bits.
•
Write Operations to Write-Only Bits/Registers
usually modify bits within other
registers. In some cases this modification is controlled by state machines. Therefore,
the effect of the write operation may not be visible, when the modified register is read
immediately after the write access that triggers the modification.
•
Reserved Bits:
Some of the bits which are contained in the XC2200’s SFRs are
marked as ‘Reserved’. User software should never write ‘1’s to reserved bits. These
bits are currently not implemented and may be used in future products to invoke new
functions. In that case, the active state for those new functions will be ‘1’, and the
inactive state will be ‘0’. Therefore writing only ‘0’s to reserved locations allows
portability of the current software to future devices. After read accesses, reserved bits
should be ignored or masked out.
Capture/Compare Unit (CAPCOM2)
The CAPCOM units support generation and control of timing sequences on up to
16 channels with a maximum resolution of 1 system clock cycle (8 cycles in staggered
mode). The CAPCOM unit is typically used to handle high speed I/O tasks such as pulse
and waveform generation, pulse width modulation (PMW), Digital to Analog (D/A)
conversion, software timing, or time recording relative to external events.
Two 16-bit timers (T7/T8) with reload registers provide two independent time bases for
each capture/compare register.
The input clock for the timers is programmable to several prescaled values of the internal
system clock, or may be derived from an overflow/underflow of timer T6 in module GPT2.
This provides a wide range of variation for the timer period and resolution and allows
precise adjustments to the application specific requirements. In addition, external count
inputs for CAPCOM timer T7 allow event scheduling for the capture/compare registers
relative to external events.
The capture/compare register array contains 16 dual purpose capture/compare
registers, each of which may be individually allocated to either CAPCOM timer T7 or T8
and programmed for capture or compare function.
All registers of each module have each one port pin associated with it which serves as
an input pin for triggering the capture function, or as an output pin to indicate the
occurrence of a compare event.