Datasheet

 
 
SBAS323G − JUNE 2004 − REVISED OCTOBER 2007
www.ti.com
36
FFh
7Fh
2Fh
2Dh
2Eh
2Ch
2Bh
2Ah
29h
28h
27h
26h
25h
24h
23h
22h
21h
20h
1Fh
18h
17h
10h
0Fh
08h
07h
7F 7E 7D 7C 7B 7A 79 78
77 76 75 74 73 72 71 70
6F 6E 6D 6C 6B 6A 69 68
67 66 65 64 63 62 61 60
5F 5E 5D 5C 5B 5A 59 58
57 56 55 54 53 52 51 50
4F 4E 4D 4C 4B 4A 49 48
47 46 45 44 43 42 41 40
3F 3E 3D 3C 3B 3A 39 38
37 36 35 34 33 32 31 30
2F 2E 2D 2C 2B 2A 29 28
27 26 25 24 23 22 21 20
1F 1E 1D 1C 1B 1A 19 18
17 16 15 14 13 12 11 10
0F 0E 0D 0C 0B 0A 09 08
07 06 05 04 03 02 01 00
0000h
Direct
RAM
Bank 3
Bit-Addressable
Bank 2
Bank 1
Bank 0
MSB LSB
Indirect
RAM
Figure 23. Scratchpad Register Addressing
Thus, an instruction can designate the value stored in R0
(for example) to address the upper RAM. The 16 bytes
immediately above the these registers are bit addressable.
So any of the 128 bits in this area can be directly accessed
using bit addressable instructions.
Stack
Another use of the Scratchpad area is for the
programmer’s stack. This area is selected using the Stack
Pointer (SP; 81h) SFR. Whenever a call or interrupt is
invoked, the return address is placed on the Stack. It also
is available to the programmer for variables, etc., since the
Stack can be moved and there is no fixed location within
the RAM designated as Stack. The Stack Pointer will
default to 07h on reset. The user can then move it as
needed. A convenient location would be the upper RAM
area (> 7Fh) since this is only available indirectly. The SP
will point to the last used value. Therefore, the next value
placed on the Stack is put at SP + 1. Each PUSH or CALL
will increment the SP by the appropriate value. Each POP
or RET will decrement as well.
Program Memory
After reset, the CPU begins execution from Program
Memory location 0000h. The selection of where Program
Memory execution begins is made by tying the EA pin to
DV
DD
for internal access, or DGND for external access.
When EA
is tied to DV
DD
, any PC fetches outside the
internal Program Memory address occur from external
memory. If EA is tied to DGND, then all PC fetches
address external memory. Table 6 shows the standard
internal Program Memory size for MSC1211/12/13/14
family members. If enabled the Boot ROM will appear from
address F800h to FFFFh.
Table 6. MSC1211/12/13/14 Maximum Internal
Program Memory Sizes
MODEL NUMBER
STANDARD INTERNAL
PROGRAM MEMORY SIZE (BYTES)
MSC121xY5 32k
MSC121xY4 16k
MSC121xY3 8k
MSC121xY2 4k