IBM EM78P447N 5 R4 RAM Select Register, 6 R5~R7 Port 5 ~ Port7, R5, R6 and R7 are I/O registers

EM78P447N

8-Bit Microcontroller with OTP ROM

4.1.4	R3 (Status Register)
7		6	5	4	3	2	1	0
GP		PS1	PS0	T	P	Z	DC	C

Bit 7 (GP) General read/write bit.

Bits 6 (PS1) ~ 5 (PS0) Page select bits. PS1~PS0 are used to pre-select a program memory page. When executing a "JMP", "CALL", or other instructions which causes the program counter to change (e.g. MOV R2, A), PS1~PS0 are loaded into the 11th and 12th bits of the program counter and select one of the available program memory pages. Note that RET (RETL, RETI) instruction does not change the PS0~PS1 bits. That is, the return will always be to the page from where the subroutine was called, regardless of the PS1~PS0 bits current setting.

PS1	PS0	Program memory page [Address]
0	0	Page 0 [000-3FF]
0	1	Page 1 [400-7FF]
1	0	Page 2 [800-BFF]
1	1	Page 3 [C00-FFF]

Bit 4 (T)		Time-out bit. Set to 1 with the "SLEP" and "WDTC" commands, or during
		power up, and reset to 0 with the WDT time-out.
Bit 3	(P)	Power down bit. Set to 1 during power on or by a "WDTC" command and
		reset to 0 by a "SLEP" command.
Bit 2	(Z)	Zero flag. Set to "1" if the result of an arithmetic or logic operation is zero.
Bit 1	(DC) Auxiliary carry flag.
Bit 0	(C)	Carry flag

4.1.5 R4 (RAM Select Register)

Bits 7~6 determine which bank is activated among the 4 banks.

Bits 5~0 are used to select the registers (address: 00~3F) in the indirect addressing mode.

If no indirect addressing is used, the RSR can be used as an 8-bit general-purpose read/writer register.

See the configuration of the data memory in Fig. 4.

4.1.6 R5~R7 (Port 5 ~ Port7)

R5, R6 and R7 are I/O registers

4.1.7 R8~R1F and R20~R3E (General Purpose Register)

R8~R1F, and R20~R3E (including Banks 0~3) are general-purpose registers.

10 • Product Specification (V1.1) 03.30.2005

(This specification is subject to change without further notice)