Samsung KS57C2308 manual Working Register Banks, Paired Working Registers

KS57C2308/P2308/C2316/P2316 ADDRESS SPACES

Working Register Banks

For addressing purposes, the working register area is divided into four register banks — bank 0, bank 1, bank 2, and bank 3. Any one of these banks can be selected as the working register bank by the register bank selection instruction (SRB n) and by setting the status of the register bank enable flag (ERB).

Generally, working register bank 0 is used for the main program, and banks 1, 2, and 3 for interrupt service routines. Following this convention helps to prevent possible data corruption during program execution due to contention in register bank addressing.

Table 2-3. Working Register Organization and Addressing

ERB Setting			SRB Settings			Selected Register Bank
	3	2		1	0
0	0	0		–	–	Always set to bank 0
				0	0	Bank 0
1	0	0		0	1	Bank 1
				1	0	Bank 2
				1	1	Bank 3

Paired Working Registers

Each of the register banks is subdivided into eight 4-bit registers. These registers, named Y, Z, W, X, H, L, E and A, can either be manipulated individually using 4-bit instructions, or together as register pairs for 8-bit data manipulation.

The names of the 8-bit register pairs in each register bank are EA, HL, WX, YZ and WL. Registers A, L, X and Z always become the lower nibble when registers are addressed as 8-bit pairs. This makes a total of eight 4-bit registers or four 8-bit double registers in each of the four working register banks.

(MSB) (LSB) (MSB) (LSB)

Y

Z

W

X

H

L

E

A

Figure 2-5. Register Pair Configuration

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