156 b EDN S
EPTEMBER 24, 1998
For most of the 683xx family, Motorola combined a stripped-
down 68020 core with a 16-bit (32-bit for CPU32+) on-chip
InterModule Bus, which links the CPU with a device’s com-
plex peripherals. The core processor, the CPU32 or CPU32+,
is a 68020 CPU for embedded control that lacks memory-
management-unit (MMU) or floating-point-unit (FPU) inter-
faces. The CPU32 and CPU32+ have 16- and 32-bit data
buses, respectively. The 32-bit processor has eight general-
purpose, 32-bit registers; seven 32-bit address registers; a 32-
bit ALU; and separate user and supervisor modes, each with
its own stack and separate address and data spaces. The
CPU32 is code-compatible with the 68020 but has enhanced
addressing modes, including scaled index; address-register
indirect with base displacement; and index, program-
counter-relative, and 32-bit branch displacements. Postin-
crement and preincrement/decrement options simplify iter-
ative code. The CPU accesses memory-mapped peripheral-
control registers and I/O as addresses in memory.
All 683xxs have a system-integration module featuring sys-
tem configuration, oscillator and clock dividers, reset and
power-down-mode control, chip selects and wait states, par-
allel I/O with interrupt capability, interrupt configuration/
response, and a software watchdog timer. The external-bus
interface has as many as 32 address and 16 data lines (32 for
CPU32+) and as many as 12 programmable chip-selection
lines. The single-chip Integration Module II allows users to
select 32-kHz or 4-MHz clock crystals.
Power management: A low-power-stop (LPSTOP) instruc-
tion stops the clock. Devices can run at low frequencies.
Special instructions: The 68020 does not support BCD-
pack/unpack, bit-field, compare-and-swap, coprocessor,
MMU, module-call/return, and memory-indirect-addressing
instructions. New instructions include a table look-up and
interpolate and the ability to put the chip into a low-power
standby mode.
Development tools: The 683xx leverages the extensive
development-tool support from the 68xxx architecture.
These tools include assemblers, compilers and debuggers,
RTOSs, emulators, and evaluation boards.
Second sources: There are no second sources for the 683xx.
Motorola 683xx
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