S3C7515/P7515

PRODUCT OVERVIEW

1-5

DATA MEMORY

Overview

The 512

× 4 bit data memory has four areas:

— 32

× 4-bit working register area

— 224

× 4-bit general-purpose area in bank 0 which is also used as the stack area

— 256

× 4-bit general-purpose area in bank 1

— 128

× 4-bit area in bank 15 for memory-mapped I/O addresses

The data memory area is also organized as three memory banks — bank 0, bank 1, and bank 15. You use the

select memory bank instruction (SMB) to select one of the banks as working data memory.

Data stored in RAM locations are 1-, 4-, and 8-bit addressable. After a hardware reset, data memory initialization

values must be defined by program code.

Data Memory Addressing Modes

The enable memory bank (EMB) flag controls the addressing mode for data memory banks 0, 1, or 15. When the

EMB flag is logic zero, only locations 00H–7FH of bank 0 and bank 15 can be accessed. When the EMB flag is

set to logic one, all three data memory banks can be accessed based on the current SMB value.

Working Registers

The RAM's working register area in data memory bank 0 is also divided into four register banks. Each register

bank has eight 4-bit registers. Paired 4-bit registers are 8-bit addressable.

Register A can be used as a 4-bit accumulator and double register EA as an 8-bit extended accumulator; double

registers WX, WL, and HL are used as address pointers for indirect addressing.

To limit the possibility of data corruption due to incorrect register addressing, it is advisable to use bank 0 for

main programs and banks 1, 2, and 3 for interrupt service routines.

Bit Sequential Carrier

The bit sequential carrier (BSC) mapped in data memory bank 15 is a 8-bit general register that you can

manipulate using 1-, 4-, and 8-bit RAM control instructions.

Using the BSC register, addresses and bit locations can be specified sequentially using 1-bit indirect addressing

instructions. In this way, a program can generate 8-bit data output by moving the bit location sequentially,

incrementing or decrementing the value of the L register. You can also use direct addressing to manipulate data

in the BSC.