Motorola CPU32 Bedienungsanleitung PDF herunterladen (Seite 25)

100

101

Introduction

1-14

M68000 FAMILY PROGRAMMER’S REFERENCE MANUAL

MOTOROLA

Address Mask

This 8-bit ﬁeld contains a mask for the address base ﬁeld. Setting a bit in this ﬁeld causes

the corresponding bit in the address base ﬁeld to be ignored. Blocks of memory larger

than 16 Mbytes can be transparently translated/access controlled by setting some logical

address mask bits to ones. The low-order bits of this ﬁeld normally are set to deﬁne con-

tiguous blocks larger than 16 Mbytes, although this not required.

E—Enable

This bit enables and disables transparent translation/access control of the block deﬁned

by this register.

0 = Transparent translation/access control disabled

1 = Transparent translation/access control enabled

S—Supervisor/User Mode

This ﬁeld speciﬁes the use of the FC2 in matching an address.

00 = Match only if FC2 is 0 (user mode access)

01 = Match only if FC2 is 1 (supervisor mode access)

1X = Ignore FC2 when matching

U1, U2—User Page Attributes

The MC68040, MC68E040, MC68LC040 do not interpret these user-deﬁned bits. If an

external bus transfer results from the access, U0 and U1 are echoed to the UPA0 and

UPA1 signals, respectively.

CM—Cache Mode

This ﬁeld selects the cache mode and access serialization for a page as follows:

00 = Cachable, Writethrough

01 = Cachable, Copyback

10 = Noncachable, Serialized

11 = Noncachable

W—Write Protect

This bit indicates if the block is write protected. If set, write and read-modify-write

accesses are aborted as if the resident bit in a table descriptor were clear.

0 = Read and write accesses permitted

1 = Write accesses not permitted

1.4 INTEGER DATA FORMATS

The operand data formats supported by the integer unit, as listed in Table 1-3, include those

supported by the MC68030 plus a new data format (16-byte block) for the MOVE16

instruction. Integer unit operands can reside in registers, memory, or instructions

themselves. The operand size for each instruction is either explicitly encoded in the

instruction or implicitly deﬁned by the instruction operation.

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