ST20-C1 View Datasheet(PDF) - STMicroelectronics
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Description
MFG CO.
'ST20-C1' PDF : 205 Pages View PDF
4.11 Peripherals and I/O
4.10.5 Other work space allocation techniques
The gajw instruction exchanges the contents of Wptr and Areg, allowing work spaces
to be allocated dynamically, and allowing dynamic switching between existing work
spaces. If a process work space holds a pointer to a new work space, then the
following code changes to the new work space and stores a pointer to the old work
space.
ldl Wnew; gajw; stl Wold;
The old work space can be restored by
ldl Wold; gajw;
In addition, the old work space can be accessed from the new work space, using
ldl Wold; ldnl x;
ldl Wold; stnl x;
ldl Wold; ldnlp x;
4.11 Peripherals and I/O
The peripheral and I/O instructions are listed in Table 4.13.
Mnemonic
Name
io
input / output
bitmask
bit mask
ldtdesc
load task descriptor
stop
stop process
Table 4.13 Peripheral and I/O instructions
4.11.1 Using the IO register
The IO register is a 32-bit register used for simple bit control of devices outside the
core. The bits of the register are directly mapped to external connections on the ST20-
C1 core. The connections to and from the IO register may be to on-chip or external
peripherals depending on the particular chip design. The bits of the IO register are
defined in Table 3.3. Some bits at the most significant end of each half word may be
reserved for the system in some ST20 variants; see the data sheet for the variant.
Setting an output bit will cause the corresponding connection to be driven high, and
clearing the bit will drive the connection low. Similarly any input or output bit may be
tested for the state of the connection; if the connection is high the bit will be set and if
the connection is low the bit will be clear.
The instruction io sets and clears bits of the IO register and loads a copy of the initial
IO register. A bit in the bottom half-word may be set in the IO register by:
ldc 0; ldc bit_number; bitmask; io;
A bit in the bottom half-word may be cleared in the IO register by:
ldc bit_number; bitmask; ldc 0; io;
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