EM77930 Datasheet, PDF (37/114 Pages) ELAN Microelectronics Corp – USB + BB Controller

EM77930
USB+BB Controller
7 Function Description
7.1 Special Purpose Registers
The special purpose registers are function-oriented registers used by the CPU to
access memory, record execution results, and carry out the desired operation. The
functions of the registers related to the core are described in the following subsections
7.1.1 Accumulator – ACC
Internal data transfer operation, or instruction operand holding usually involves the
temporary storage function of the Accumulator, which is not an addressable register.
7.1.2 Indirect Addressing Contents – IAC0 (0x00) and IAC1 (0x09)
The contents of R0 and R9 are implemented as indirect addressing pointers if any
instruction uses R6 and R8 as registers.
7.1.3 Program Counter HPC (0x01) and LPC (0x02)
„ The Program Counter (PC) is composed of registers HPC and LPC.
„ The PC and the hardware stacks are 14 bits wide.
„ The structure is depicted in Fig. 6-1.
„ Generates 12K × 16 on-chip ROM addresses to the corresponding program
memory (ROM).
„ All the bits of PC are set to "0"s as a reset condition occurs.
„ "RET" ("RETL k", "RETI") instruction loads the program counter with the contents
at the top of the stack.
„ "MOV R2, A" allows the loading of an address from the "A" register to the lower 8
bits of the PC, and the high byte (A8~A14) of the PC remain unchanged.
„ "ADD R2, A" & "TBL" allows a corresponding address / offset to be added to the
current PC.
7.1.4 Status Register –SR (0x03)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
-
-
RST
T
P
Z
DC
C
Bit 0 (C): Carry flag. This bit indicates that a carry out of ALU occurred during the last
arithmetic operation. This bit is also affected during bit test, branch
instruction and during bit shifts.
Bit 1 (DC): Auxiliary carry flag. This bit is set during ADD and ADC operations to
indicate that a carry occurred between Bit 3 and Bit 4.
Product Specification (V1.0) 08.20.2007
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(This specification is subject to change without further notice)