MC68EC000 Motorola, MC68EC000 Datasheet - Page 88

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

bit was not modified). External memory management hardware should not treat the access
in the old FC space as an error.
4.1.4 Reference Classification
When the SCM68000 makes a reference, it classifies the reference according to the encod-
ing of the three function code output lines. This classification allows external translation of
addresses, control of access, and differentiation of special SCM68000 states, such as CPU
space (used by interrupt acknowledge cycles). Table 4-1 lists the classification of refer-
ences.
4.1.5 CPU Space Cycle
A CPU space cycle, indicated when the function codes are all high, is a special cycle. Bits
A19–A16 of the address bus identify sixteen types of CPU space cycles. The interrupt
acknowledge cycle, in which A19–A16 are high, is currently the only defined CPU space
cycle for the SCM68000. Other configurations of A19–A16 are reserved by Motorola to
define other types of CPU cycles used in other M68000 Family microprocessors. Figure 4-
1 shows the encoding of CPU space addresses.
4.1.5.1 INTERRUPT ACKNOWLEDGE CYCLE. The interrupt acknowledge cycle places
the level of the interrupt being acknowledged on address bits A3–A1 and drives all other ad-
dress lines high. For a vectored interrupt, the interrupt acknowledge cycle reads a vector
number when the interrupting device places a vector number on the data bus and asserts
DTACKB to acknowledge the cycle. The timing diagram for a vectored interrupt is shown in
Figure 4-2.
MOTOROLA
ACKNOWLEDGE
INTERRUPT
FUNCTION
1
2
CODE
1
*
4 are reserved for future use by Motorola.
Figure 4-1. CPU Space Address Encoding
1
0
Address space 3 is reserved for user definition, while 0 and
Freescale Semiconductor, Inc.
FC2
EC000 CORE PROCESSOR USER’S MANUAL
Function Code Output
0
0
0
0
1
1
1
1
For More Information On This Product,
Table 4-1. Reference Classification
31
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
FC1
0
0
1
1
0
0
1
1
Go to: www.freescale.com
FC0
0
1
0
1
0
1
0
1
ADDRESS BUS
CPU SPACE
TYPE FIELD
19
Supervisor Program
Address Space
Supervisor Data
User Program
(Undefined)
(Reserved)
(Reserved)
CPU Space
User Data
16
*
*
*
Exception Processing
3
LEVEL
1
0
1
4-3