Texas Instruments MSC1210 manual Bit Memory

Internal RAM

But watch out! As the memory map shows, the MSC1210 has four distinct register banks. When the MSC1210 is first reset, register bank 0 (addresses 00H through 07H) is used by default. However, the MSC1210 may be instructed to use one of the alternate register banks (i.e., register banks 1, 2, or 3). In this case, R4 will no longer be the same as internal RAM address 04H. For example, if the program instructs the 8052 to use register bank 1, register R4 is now synonymous with internal RAM address 0CH. If register bank 2 is selected, R4 is synonymous with 14H, and if register bank 3 is selected, it is synonymous with address 1CH.

The concept of register banks adds a great level of flexibility to the 8052, espe- cially when dealing with interrupts (see chapter 10, Interrupts, for details). However, always remember that the register banks really reside in the first 32 bytes of internal RAM.

Note:

If only the first register bank (i.e. bank 0) is used, internal RAM locations 08H through 1FH can be used by the program for its own use. If register banks 1, 2, or 3 are to be used, be very careful about using addresses below 20H to avoid overwriting the value of “R” registers from other register banks.

2.4.3Bit Memory

The MSC1210, being a communications and control-oriented microcontroller that often has to deal with on and off situations, gives you the ability to access a number of bit variables directly with simple instructions to set, clear, and compare these bits. These variables may be either 1 or 0.

There are 128 bit variables available to the user, numbered 00H through 7FH. The user may make use of these variables with commands such as SETB and CLR. For example, to set bit number 24H (hex) to 1, the user would execute the instruction:

SETB 24h

It is important to note that Bit memory, like the register banks in section 2.4.2, is really a part of internal RAM. In fact, the 128-bit variables occupy the 16 by- tes of internal RAM from 20H through 2FH. Thus, if the value FFH is written to internal RAM address 20H, bits 00H through 07H have been effectively set. That is to say that the instruction:

MOV 20h,#0FFh

is equivalent to the instructions:

SETB 00h

SETB 01h

SETB 02h

SETB 03h

SETB 04h

SETB 05h

SETB 06h

SETB 07h

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