DS80C320-MCG Datasheet, PDF (4/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

High-Speed Microcontroller User’s Guide
retains the value which software writes. In general, during a read operation, software reads the state of
the external pin. Each port is represented by a SFR location.
Timer/Counters
Three 16-bit Timer/Counters are available in the High-Speed Microcontroller. Each timer is contained in
two SFR locations that can be written or read by software. The timers are controlled by other SFRs
described in Section 4.
UARTs
The High-Speed Microcontroller provides one or two UARTs. These are controlled and accessed as
SFRs. Each UART has an address that is used to read or write the UART. The same address is used for
both read and write operations. The microcontroller distinguishes between a read and a write by the
instruction. Each UART is controlled by its own SFR control register.
SCRATCHPAD REGISTERS (RAM)
The High-Speed Core provides 256 bytes of Scratchpad RAM for general purpose data and variable
storage. The first 128 bytes are directly available to software. The second 128 are available through
indirect addressing discussed below. Selected portions of this RAM have other optional functions.
Stack
The stack is a RAM area that the microcontroller uses to store return address information during Calls
and Interrupts. The user can also place variables on the stack when necessary. The Stack Pointer
mentioned above designates the RAM location that is the top of the stack. Thus, depending on the value
of the Stack Pointer, the stack can be located anywhere in the 256 bytes of RAM. A common location
would be in the upper 128 bytes of RAM, as these are accessible through indirect addressing only.
Working Registers
The first thirty-two bytes of the Scratchpad RAM can be used as four banks of eight Working Registers
for high speed data movement. Using four banks, software can quickly change context by simply
changing to a different bank. In addition to the Accumulator, the Working Registers are commonly used
as data source or destination. Some of the Working Registers can also be used as pointers to other RAM
locations (indirect addressing).
PROGRAM COUNTER
The Program Counter (PC) is a 16-bit value that designates the next program address to be fetched. On-
chip hardware automatically increments the PC value to move to the next ROM location.
ADDRESS/DATA BUS
The High-Speed Microcontroller addresses a 64KB program and 64KB data memory area. In the
ROMless versions, all memory is outside. Other versions use a combination of internal and external
memory. When external memory is accessed, Ports 0 and 2 are used as a multiplexed address and data
bus. Port 2 provides the address MSB. Even versions with internal memory can use the bus on Ports 0
and 2 to access more memory.
WATCHDOG TIMER
The Watchdog Timer provides a supervisory function for applications that cannot afford to run out of
control. The Watchdog Timer is a programmable free running timer. If allowed to reach the termination
of its count, if enabled, the Watchdog will reset the CPU. Software must prevent this by cleaning or
resetting the Watchdog prior to its time-out.
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