MC68HC705KJ1 Datasheet, PDF (25/108 Pages) Motorola, Inc – HCMOS Microcontroller Unit

RAM
2.6 RAM
The 64 addresses from $00C0 to $00FF serve as both the user RAM and the stack RAM. Before
processing an interrupt, the CPU uses five bytes of the stack to save the contents of the CPU registers.
During a subroutine call, the CPU uses two bytes of the stack to store the return address. The stack
pointer decrements when the CPU stores a byte on the stack and increments when the CPU retrieves a
byte from the stack.
NOTE
Be careful when using nested subroutines or multiple interrupt levels. The
CPU may overwrite data in the RAM during a subroutine or during the
interrupt stacking operation.
2.7 EPROM/OTPROM
An MCU with a quartz window has 1240 bytes of erasable, programmable ROM (EPROM). The quartz
window allows EPROM erasure with ultraviolet light.
NOTE
Keep the quartz window covered with an opaque material except when
erasing the MCU. Ambient light can affect MCU operation.
In an MCU without the quartz window, the EPROM cannot be erased and serves as 1240 bytes of
one-time programmable ROM (OTPROM).
The following addresses are user EPROM/OTPROM locations:
• $0300–$07CF
• $07F8–$07FF, used for user-defined interrupt and reset vectors
The COP register (COPR) is an EPROM/OTPROM location at address $07F0.
The mask option register (MOR) is an EPROM/OTPROM location at address $07F1.
2.7.1 EPROM/OTPROM Programming
The two ways to program the EPROM/OTPROM are:
• Manipulating the control bits in the EPROM programming register to program the
EPROM/OTPROM on a byte-by-byte basis
• Programming the EPROM/OTPROM with the M68HC705J In-Circuit Simulator (M68HC705JICS)
available from Freescale
MC68HC705KJ1 • MC68HRC705KJ1 • MC68HLC705KJ1 Data Sheet, Rev. 4.1
Freescale Semiconductor
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