KSI-W002-000

7

6.3 Data Memory (RAM)

Data memory is used to store various type of processing data. This consists of a 32-nibble,

which is organized into two files of 16 nibbles each. RAM addressing is indirectly

implemented by a two registers; H, L. It’s upper 1-bit register (H) selects one of two files

and its lower 4-bit register (L) selects one of 16 nibbles in the selected file.

Figure 6-2. Data Memory Map

6.4 Stack Register (SK)

Stack register is used to store return address and provide a particularly mechanism for

transferring control between programs. Two level hardware push/pop stacks are

manipulated by CAL, CALL, and RET instructions. CAL/CALL instructions push the current

program counter value, incremented by “1”, into stack level 1. Stack level 1 is

automatically pushed to level 2.

If more than two subsequent CAL/CALL are executed, only the most recent two return

addresses are stored. RET instruction load the contents of stack level 1 into the program

counter while stack level 2 gets copied into level 1. If more than two subsequent RET are

executed, the stack will be filled with the address previously stored in level 2.

SD6830

REG H (1-bit)

REG L ( 4-bit )

PORT

F

F0

FILE 1

0

1

2

3

12

13

14

15

Lower

3-bit

4

F1

F2

F3

F4

F5

F6

F7

DATA MEMORY

FILE 0

0

1

2

3

12

13

14

15