MC68EC000 Motorola, MC68EC000 Datasheet - Page 21

• Manufacturer Part Number: MC68EC000
• Description: Core Processor (SCM 68000)
• Manufacturer: Motorola

Overview
The user mode (see Figure 1-3(a)) provides access to 16 32-bit general-purpose registers
(D0–D7, A0–A7), a 32-bit program counter, and an 8-bit condition code register. The first
eight registers (D0–D7) are used as data registers for byte (8-bit), word (16-bit), and long-
word (32-bit) operations. The second set of seven registers (A0–A6) and the user stack
pointer (A7/USP) can be used as software stack pointers and base address registers. In
addition, the address registers can be used for word and long-word operations. All of the 16
registers can be used as index registers.
The supervisor mode (see Figure 1-3(b)) provides access to two supplementary registers,
the status register (high-order byte) and the supervisor stack pointer (A7'/SSP). The status
register (SR) (see Figure 1-4) contains the interrupt mask (eight levels available) and the
following condition codes: overflow (V), zero (Z), negative (N), carry (C), and extend (X).
Additional status bits indicate whether the SCM68000 is in the trace (T) mode and/or in the
supervisor (S) state. Bits 5, 6, 7, 11, 12, and 14 are undefined and reserved for future expan-
sion.
1-8
TRACE MODE
SUPERVISOR
INTERRUPT
STATE
MASK
15
T
Freescale Semiconductor, Inc.
EC000 CORE PROCESSOR USER’S MANUAL
13
S
SYSTEM BYTE
For More Information On This Product,
Figure 1-4. Status Register
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10
I
2
I
1 0
I
8
USER BYTE
4
X N Z V C
0
EXTEND
NEGATIVE
ZERO
OVERFLOW
CARRY
CONDITION
CODES
MOTOROLA