Texas Instruments MSP50C6xx manual Data Memory Address and Data Relationship, Movb A0, *0x0003

Bit, Byte, Word and String Addressing

Flag Address: The flag (or TAG) address uses linear addressing from 0 to the size of data memory in 17-bit wide words (0 to 639 for MSP50P614/ MSP50C614). Only the 17th bit is accessible. When a word memory location is read, the corresponding flag for that location is always loaded into the TAG bit of the status register (STAT). The flag address always corresponds to a 17-bit wide word address. If string instructions are used, then the flag bit of the last memory location of the string is loaded into the TAG bit of the status regis- ter. Global flag addressing or relative flag addressing is used to address flags. Flag bits can be set or reset using flag instructions in addition to various logical operations. The flag address does not have a string mode.

Rx Post Modifications: Indirect addressing allows post modification of Rx. For byte and byte-string mode, Rx is post modified by 1 for each byte. For word and word-string mode Rx is post modified by 2 for each word. Post modification of Rx is not available for flag addressing.

Table 4–40. Data Memory Address and Data Relationship

Mode	Address Used	Data Order	Rx Post modify†
Single byte	Absolute 16-bit address	8-bit data	1
Byte string	Beginning of string at lower address	String length times 8-bit data	1 per byte in string
		by Incrementing addresses
Single word	Even address, if odd address is used,	16-bit data	2
	the LSB bit of address is assumed 0
Word string	Even address beginning at a lower	String length times 16-bit data	2 per word in
	address; if odd address is used, the	by incrementing addresses	string
	LSB bit of address is assumed 0
Flag	Address is considered as holding 17-bit	1-bit data	not available
	data, but only 17th bit is accessed.

† Rx post modification is available by various addressing modes (see 4.3, Instruction Syntax and Addressing Modes for detail).

Example 4.5.1 MOVB A0, *0x0003

Refer to Figure 4–4 for this example. This instruction loads the value 0x78 to the accumulator. The upper 8 bits of the accumulator is padded with zeros.

Example 4.5.2	MOV	A0,	*0x0000
	MOV	A0,	*0x0001

Refer to Figure 4–4 for this example. Both instructions will load the value 0x1234 to the accumulator. In word addressing, the LSB bit of the address is assumed to be zero. Thus, in the second instruction, the least significant bit of the address is ignored.

Example 4.5.3 MOV A0, *0x0004 * 2

Refer to Figure 4–4 for this example. The word address 0x0004 is referred. Multiplication by 2 is necessary to convert the word address into the equivalent byte address . After multiplication, the byte address is 0x0008. This instruction will load the value 0x1122 to the accumulator.

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