ELAN Home Systems EM78P458 - Manual (Page 8)

EM78P458/459
OTP ROM
4. FUNCTION DESCRIPTION
DATA & CONTROL BUS
IOC5
R5
P
5
0 P
5
1 P
5
2 P
5
3 P
5
4 P
5
5 P
5
6 P
5
7
Comparators 8 ADC 2 PWMs
IOC6
R6
P
6
0 P
6
1 P
6
2 P
6
3 P
6
4 P
6
5 P
6
6 P
6
7
ACC R3
STACK 0
STACK 1
STACK 2
STACK 3
STACK 4
P C
ROM
Instruction
Register
Instruction
Decoder
ALU
Interrupt
Control
/INT
R4
RAM
WDT Timer
Prescaler
Oscillator/
Timming
Control
WDT
Time-out
R1(TCC)
Sleep
&
Wake Up
Control
ENTCC
STACK 5
STACK 6
STACK 7
Fig. 2 The Functional Block Diagram of EM78P458/459
4.1 Operational Registers
1. R0 (Indirect Addressing Register)
R0 is not a physically implemented register. Its major function is to perform as an indirect addressing
pointer. Any instruction using R0 as a pointer, actually accesses data pointed by the RAM Select
Register (R4).
2. R1 (Time Clock /Counter)
• Increased by an external signal edge through the TCC pin, or by the instruction cycle clock.
• The signals to increase the counter are decided by Bit 4 and Bit 5 of the CONT register.
• Writable and readable as any other registers.
3. R2 (Program Counter) & Stack
• R2 and hardware stacks are 12-bit wide. The structure is depicted in Fig. 4.
• Generates 4K ×13 bits on-chip ROM addresses to the relative programming instruction codes. One
program page is 1024 words long.
This specification is subject to change without prior notice. 07.01.2003 (V1.3) 8