UPD75518 NEC, UPD75518 Datasheet - Page 27

• Manufacturer Part Number: UPD75518
• Description: 4 BIT SINGLE-CHIP MICROCOMPUTER
• Manufacturer: NEC

3. INTERNAL CPU FUNCTIONS
3.1 PROGRAM COUNTER (PC): 15 BITS
a RESET input sets the low-order six bits of program memory address 0000H in PC13 to PC8, and the contents
of address 0001H in PC7 to PC0, and 0 in PC14 for initialization.
3.2 PROGRAM MEMORY (ROM): 32640 WORDS
programs, table data, and so forth.
reference instruction (MOVT).
instructions. The whole-space branch instruction (BRA !addr1) and the whole-space call instruction (CALLA
!addr1) allow a direct branch throughout the whole space 0000H to 5F7FH. The relative branch instruction
(BR $addr) allows a branch to addresses (PC - 15 to PC - 1 and PC + 2 to PC + 16) regardless of block boundaries.
addresses. (All areas excluding 0000H and 0001H can be used as normal program memory.)
• 0000H to 0001H
• 0002H to 000DH
• 0020H to 007FH
Vector table for holding the RBE and MBE setting values and program start address at the time of a RESET
input. A reset start can be performed at an arbitrary address within a 16K-byte space (0000H to 3FFFH).
Vector table for holding the RBE and MBE setting values and program start address at the time of each
vectored interrupt occurrence. Interrupt processing can be started at an arbitrary address within a 16K-
byte space (0000H to 3FFFH).
Table area referenced by the GETI instruction
The program counter is a 15-bit binary counter for holding program memory address information.
Note that the reset start address must be set within a space of 16K bytes (0000H to 3FFFH). This is because
The program memory is a mask-programmable ROM with a configuration of 32640 words 8 bits for storing
Program memory is addressed by the program counter. Table data can be referenced using the table
Fig. 3-2 shows the allowable branch address ranges for the branch instructions and subroutine call
The program memory is located at addresses 0000H to 5F7FH containing the following specially assigned
Note The GETI instruction can represent an arbitrary 2-byte or 3-byte instruction or two 1-byte instructions
PC14
in 1 byte, thus reducing the number of program steps. (See Section 8.1.)
PC13
PC12 PC11
PC10
Fig. 3-1 Program Counter Format
PC9
PC8
Note
PC7
8 BITS
PC6
PC5
PC4
PC3
PC2
PD75518(A)
PC1
PC0
PC
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