MC9S12XD256MAL Datasheet, PDF (215/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Chapter 6 XGATE (S12XGATEV2)
6.8.3 Cycle Notation
Table 6-16 show the XGATE access detail notation. Each code letter equals one XGATE cycle. Each letter
implies additional wait cycles if memories or peripherals are not accessible. Memories or peripherals are
not accessible if they are blocked by the S12X_CPU. In addition to this Peripherals are only accessible
every other XGATE cycle. Uppercase letters denote 16 bit operations. Lowercase letters denote 8 bit
operations. The XGATE is able to perform two bus or wait cycles per S12X_CPU cycle.
Table 6-16. Access Detail Notation
V — Vector fetch: always an aligned word read, lasts for at least one RISC core cycle
P — Program word fetch: always an aligned word read, lasts for at least one RISC core cycle
r — 8 bit data read: lasts for at least one RISC core cycle
R — 16 bit data read: lasts for at least one RISC core cycle
w — 8 bit data write: lasts for at least one RISC core cycle
W — 16 bit data write: lasts for at least one RISC core cycle
A — Alignment cycle: no read or write, lasts for zero or one RISC core cycles
f — Free cycle: no read or write, lasts for one RISC core cycles
Special Cases
PP/P — Branch: PP if branch taken, P if not
6.8.4 Thread Execution
When the RISC core is triggered by an interrupt request (see Figure 6-1) it first executes a vector fetch
sequence which performs three bus accesses:
1. A V-cycle to fetch the initial content of the program counter.
2. A V-cycle to fetch the initial content of the data segment pointer (R1).
3. A P-cycle to load the initial opcode.
Afterwards a sequence of instructions (thread) is executed which is terminated by an "RTS" instruction. If
further interrupt requests are pending after a thread has been terminated, a new vector fetch will be
performed. Otherwise the RISC core will idle until a new interrupt request is received. A thread can not be
interrupted by an interrupt request.
6.8.5 Instruction Glossary
This section describes the XGATE instruction set in alphabetical order.
MC9S12XDP512 Data Sheet, Rev. 2.21
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