P912XDP512F0MPVR datasheet(203/1348 Pages) FREESCALE

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Chapter 6 XGATE (S12XGATEV2)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

203

The programmer’s model of the XGATE RISC core is shown in Figure 6-19. The processor offers a set of

seven general purpose registers (R1 - R7), which serve as accumulators and index registers. An additional

eighth register (R0) is tied to the value “$0000”. Register R1 has an additional functionality. It is preloaded

with the initial variable pointer of the channel’s service request vector (see Figure 6-20). The initial content

of the remaining general purpose registers is undeﬁned.

The 16 bit program counter allows the addressing of a 64 kbyte address space.

The condition code register contains four bits: the sign bit (S), the zero ﬂag (Z), the overﬂow ﬂag (V), and

the carry bit (C). The initial content of the condition code register is undeﬁned.

6.4.3

Memory Map

The XGATE’s RISC core is able to access an address space of 64K bytes. The allocation of memory blocks

within this address space is determined on chip level. Refer to the S12X_MMC Section for a detailed

information.

The XGATE vector block assigns a start address and a variable pointer to each XGATE channel. Its

position in the XGATE memory map can be adjusted through the XGVBR register (see Section 6.3.1.3,

“XGATE Vector Base Address Register (XGVBR)”). Figure 6-20 shows the layout of the vector block.

Each vector consists of two 16 bit words. The ﬁrst contains the start address of the service routine. This

value will be loaded into the program counter before a service routine is executed. The second word is a

pointer to the service routine’s variable space. This value will be loaded into register R1 before a service

routine is executed.

Figure 6-20. XGATE Vector Block

+$0000

unused

+$0024

+$0028

+$002C

+$0030

+$01E0

Code

Variables

Code

Variables

XGVBR

Channel $0A Initial Program Counter

Channel $0A Initial Variable Pointer

Channel $09 Initial Program Counter

Channel $09 Initial Variable Pointer

Channel $0B Initial Program Counter

Channel $0B Initial Variable Pointer

Channel $0C Initial Program Counter

Channel $0C Initial Variable Pointer

Channel $78 Initial Program Counter

Channel $78 Initial Variable Pointer

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