15
12
11
10
7
6
5
4
3
0
0
0
0
1
1
Source bits 19:16
A/L
0
0
Destination bits 19:16
15
12
11
10
9
8
7
6
5
4
3
0
0001
1
00
ZC
#
A/L
0
0
(n−1)/Rn
MSP430 and MSP430X Instructions
146
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
CPUX
4.5.2 MSP430X Extended Instructions
The extended MSP430X instructions give the MSP430X CPU full access to its 20-bit address space. Most
MSP430X instructions require an additional word of op-code called the extension word. Some extended
instructions do not require an additional word and are noted in the instruction description. All addresses,
indexes, and immediate numbers have 20-bit values when preceded by the extension word.
There are 2 types of extension words:
•
Register or register mode for Format I instructions and register mode for Format II instructions
•
Extension word for all other address mode combinations
4.5.2.1
Register Mode Extension Word
The register mode extension word is shown in
and described in
. An example is
shown in
Figure 4-25. Extension Word for Register Modes
Table 4-11. Description of the Extension Word Bits for Register Mode
Bit
Description
15:11
Extension word op-code. Op-codes 1800h to 1FFFh are extension words.
10:9
Reserved
ZC
Zero carry
0
The executed instruction uses the status of the carry bit C.
1
The executed instruction uses the carry bit as 0. The carry bit is defined by the result of the final operation after
instruction execution.
#
Repetition
0
The number of instruction repetitions is set by extension word bits 3:0.
1
The number of instruction repetitions is defined by the value of the 4 LSBs of Rn. See description for bits 3:0.
A/L
Data length extension. Together with the B/W bits of the following MSP430 instruction, the AL bit defines the used data
length of the instruction.
A/L
B/W
Comment
0
0
Reserved
0
1
20-bit address word
1
0
16-bit word
1
1
8-bit byte
5:4
Reserved
3:0
Repetition count
# = 0
These 4 bits set the repetition count n. These bits contain n – 1.
# = 1
These 4 bits define the CPU register whose bits 3:0 set the number of repetitions. Rn.3:0 contain n – 1.
4.5.2.2
Non-Register Mode Extension Word
The extension word for non-register modes is shown in
and described in
. An
example is shown in
Figure 4-26. Extension Word for Non-Register Modes