2 data memory, 1 data memory addressing, Index register ix – Epson 6200A User Manual

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EPSON

S1C6200/6200A CORE CPU MANUAL

2 MEMORY AND OPERATIONS

2.2 Data Memory

The data memory area comprises 4,096 4-bit words. The RAM, timer, I/O and other peripheral circuits are
mapped into this memory according to the designer's specifications. Figure 2.2.1 shows the data memory
configuration.

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Page 15

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Page 14

Step 0
Step 1

Step 254
Step 255

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Page 3

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Page 2

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Page 1

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Page 0

Step 0
Step 1

Step 15

Step 254
Step 255

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XHL or YHL

(within page)

4-bit data

Memory or I/O

XP or YP

(page specification)

Page 0
only

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Fig. 2.2.1 Data memory configuration

2.2.1 Data memory addressing

The following registers and pointers, which are described in detail below, are used to address the data
memory.

Table 2.2.1.1 Registers and pointer for data memory addressing

Index Register X

Index Register Y

Stack Pointer

Mnemonic

Size (bits)

• Index register IX

Index register IX has a 4-bit page part (XP) and an 8-
bit register (XHL), and can address any location in
the data memory. See Figure 2.2.1.1.

XHL is divided into two 4-bit groups: the four high-
order bits (XH) and the four low-order bits (XL), and
can address any location within a page.

Fig. 2.2.1.1 The configuration of the index register IX

–

MX is the data memory location whose address is specified by IX.

–

M(X) refers to the contents of the data memory location whose address is specified by IX.

–

XHL can be incremented by 1 or 2 using a post-increment instruction (LDPX, ACPX, SCPX, LBPX or
RETD). An overflow occurring in XHL does not affect the flags.

MSB

LSB