MC68030 Datasheet, PDF (365/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Coprocessor Interface Description
The encoding of bits 0-8 of the coprocessor instruction operation word is dependent on the
particular instruction being implemented (see 10.2 Coprocessor Instruction Types).
10.1.4 Coprocessor System Interface
The communication protocol between the main processor and coprocessor necessary to
execute a coprocessor instruction uses a group of interface registers, called coprocessor
interface registers, resident within the coprocessor. By accessing one of these interface
registers, the MC68030 hardware initiates coprocessor instructions. The coprocessor uses
a set of response primitive codes and format codes defined for the M68000 coprocessor
interface to communicate status and service requests to the main processor through these
registers. The coprocessor interface registers (CIRs) are also used to pass operands
between the main processor and the coprocessor. The CIR set, response primitives, and
format codes are discussed in 10.3 Coprocessor Interface Register Set and 10.4
Coprocessor Response Primitives.
10.1.4.1 COPROCESSOR CLASSIFICATION. M68000 coprocessors can be classified
into two categories depending on their bus interface capabilities. The first category, non-
DMA coprocessors, consists of coprocessors that always operate as bus slaves. The
second category, DMA coprocessors, consists of coprocessors that operate as bus slaves
while communicating with the main processor across the coprocessor interface, but also
have the ability to operate as bus masters, directly controlling the system bus.
If the operation of a coprocessor does not require a large portion of the available bus
bandwidth or has special requirements not directly satisfied by the main processor, that
coprocessor can be efficiently implemented as a non-DMA coprocessor. Since non-DMA
coprocessors always operate as bus slaves, all external bus-related functions that the
coprocessor requires are performed by the main processor. The main processor transfers
operands from the coprocessor by reading the operand from the appropriate CIR and then
writing the operand to a specified effective address with the appropriate address space
specified on the function code lines. Likewise, the main processor transfers operands to the
coprocessor by reading the operand from a specified effective address (and address space)
and then writing that operand to the appropriate CIR using the coprocessor interface. The
bus interface circuitry of a coprocessor operating as a bus slave is not as complex as that
of a device operating as a bus master.
MOTOROLA
MC68030 USER’S MANUAL
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