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Rev. 1.00
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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
RAM Data Memory
Register Banks
There are four register banks, with addresses from 00H to 1FH, with each bank containing eight
bytes. The active bank is selected by the control bits, RS1 and RS0, in the PSW register. It should
be noted that only one bank can be enabled at any time. This total of 32 bytes are used as General
Purpose data memory, which can be accessed by either direct or indirect instructions.
Bit Addressable Space
Some instructions in the 8051 language allow for single bit addressing. These single bit instructions
can only be used in the bit addressable data memory area, located both in the General Purpose Data
RAM and the Special Function Register area. Note that these bit addressable registers are both byte
and bit addressable.
The 16 bytes bit addressable registers of the General Purpose Data RAM, located from 20H to
2FH, can address up to 128 individual bits. Each bit has its corresponding bit address from 00H
to 7FH. For example, bit 0 of the 20H register is mapped to the bit address 00H, bit 7 of the 20H
register is mapped to the bit address 07H and bit 7 of the 2FH register is mapped to the bit address
7FH. The accompanying table illustrates the Bit-Addressable register map description for General
Purpose Data RAM, 20H~2FH. Using the bit operational instruction, such as SETB or CLR on the
bit address can implement operations on the corresponding bit of the register. For example:
SETB 00H
; Set the bit 0 of the register location 20H to “1”
SETB 07H
; Set the bit 7 of the register location 20H to “1”
CLR 25H
; Clear the bit 5 of the register location 24H to “0”
CLR 7FH
; Clear the bit 7 of the register location 2FH to “0”
General Purpose Data RAM, 20H~2FH, Bit Address Map
High 5-bit
Address
Low 3-bit Address
0H
1H
2H
3H
4H
5H
6H
7H
78H
0x�F.0
0x�F.1
0x�F.�
0x�F.3
0x�F.4
0x�F.�
0x�F.6
0x�F.7
70H
0x�E.0
0x�E.1
0x�E.�
0x�E.3
0x�E.4
0x�E.�
0x�E.6
0x�E.7
68H
0x�D.0
0x�D.1
0x�D.�
0x�D.3
0x�D.4
0x�D.�
0x�D.6
0x�D.7
60H
0x�C.0
0x�C.1
0x�C.�
0x�C.3
0x�C.4
0x�C.�
0x�C.6
0x�C.7
�8H
0x�B.0
0x�B.1
0x�B.�
0x�B.3
0x�B.4
0x�B.�
0x�B.6
0x�B.7
�0H
0x�A.0
0x�A.1
0x�A.�
0x�A.3
0x�A.4
0x�A.�
0x�A.6
0x�A.7
48H
0x�9.0
0x�9.1
0x�9.�
0x�9.3
0x�9.4
0x�9.�
0x�9.6
0x�9.7
40H
0x�8.0
0x�8.1
0x�8.�
0x�8.3
0x�8.4
0x�8.�
0x�8.6
0x�8.7
38H
0x�7.0
0x�7.1
0x�7.�
0x�7.3
0x�7.4
0x�7.�
0x�7.6
0x�7.7
30H
0x�6.0
0x�6.1
0x�6.�
0x�6.3
0x�6.4
0x�6.�
0x�6.6
0x�6.7
�8H
0x��.0
0x��.1
0x��.�
0x��.3
0x��.4
0x��.�
0x��.6
0x��.7
�0H
0x�4.0
0x�4.1
0x�4.�
0x�4.3
0x�4.4
0x�4.�
0x�4.6
0x�4.7
18H
0x�3.0
0x�3.1
0x�3.�
0x�3.3
0x�3.4
0x�3.�
0x�3.6
0x�3.7
10H
0x��.0
0x��.1
0x��.�
0x��.3
0x��.4
0x��.�
0x��.6
0x��.7
08H
0x�1.0
0x�1.1
0x�1.�
0x�1.3
0x�1.4
0x�1.�
0x�1.6
0x�1.7
00H
0x�0.0
0x�0.1
0x�0.�
0x�0.3
0x�0.4
0x�0.�
0x�0.6
0x�0.7