SC73C1402

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.1

2005.12.19

Http: www.silan.com.cn

Page 6 of 20

6. LR

LR refers to the L register (4 bits). It is often used to store the pointer of RAM addresses, and can also be

used as a general-purpose register.

7. RAM

RAM refers to data memory. It consists of 16 x 4bits and is used to store temporary data and results after a

program is executed. There are two RAM addressing modes: one for indirect addressing by the LR register, it

can address the entire RAM areas. The other is instruction direct addressing, the lower 3-bit of the instruction

specifying the address of the RAM. It can be used to address the lower 8-bit of the RAM, but SC73C1402 does

not support this mode. When reset, the contents of RAM are not defined. We recommend users to initialize it at

the beginning of the program.

8. ALU

The arithmetic and logic unit plays a leading role in performing various operations of 4-bit binaries. The

operation of the ALU will change the carry flag and the zero flag.

9. Acc

4-bit accumulator, it is mostly used to store data and results.

10. CF

CF refers to carry flag.

11. SF

SF refers to the status flag. When reset, the status flag is initialized to 1.

12. PR

PR refers to the port register, which specifies the input mode or output mode of the I/O ports, is 4-bit write-

only. When one bit of PR is 1, the corresponding port is set to output mode; if the bit of PR is 0; then set to input

mode. The execution of the HOLD instruction won’

t affect the status of PORT1 and PORT2. When reset, the

value of the PR is 0000B.

PORT2 mode select

P2S

P1HS

P1LS

P13, P12 mode select

P11, P10 mode select

13. PORT

SC73C1402 has five groups of I/O ports, altogether 20 pins.

P0 port: P03~P00, 4-bit input port, with internal pull-down resistor; it can release the HOLD mode at high

level.

P1 port (P13~P10) and P2 port (P23~P20) can be set to input/output mode by program. In input mode, it

can release HOLD mode at high level.

P3 port (P30~P33) output port.

P5 port (P53, P52, P51, P50)

P50: output pin, P-channel open-drain output, this pin is always used to select system code.