PIC18F87J11_12 Datasheet, PDF (70/466 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Flash Microcontrollers

PIC18F87J11 FAMILY
6.1.4
EXTENDED MICROCONTROLLER
MODE AND ADDRESS SHIFTING
By default, devices in Extended Microcontroller mode
directly present the Program Counter value on the
external address bus for those addresses in the range
of the external memory space. In practical terms, this
means addresses in the external memory device below
the top of on-chip memory are unavailable.
To avoid this, the Extended Microcontroller mode
implements an address shifting option to enable auto-
matic address translation. In this mode, addresses
presented on the external bus are shifted down by the
size of the on-chip program memory and are remapped
to start at 0000h. This allows the complete use of the
external memory device’s memory space as an
extension of the device’s on-chip program memory.
FIGURE 6-3:
MEMORY MAPS FOR PIC18F87J11 FAMILY PROGRAM MEMORY MODES
Microcontroller Mode⁽¹⁾
Extended Microcontroller Mode⁽²⁾
Extended Microcontroller Mode
with Address Shifting⁽²⁾
On-Chip
Memory
Space
000000h
On-Chip
Program
Memory
(Top of Memory)
(Top of Memory) + 1
External
Memory
Space
No
Access
Reads
as ‘0’s
External
Memory
On-Chip
Memory
Space
000000h
On-Chip
Program
Memory
(Top of Memory)
(Top of Memory) + 1
External
Memory
Space
External
Memory
Mapped
to
External
Memory
Space
On-Chip
Memory
Space
000000h
On-Chip
Program
Memory
(Top of Memory)
(Top of Memory) + 1⁽³⁾
Mapped
to
External
Memory
Space
1FFFFFh –
(Top of Memory)
1FFFFFh
1FFFFFh
1FFFFFh
Legend: (Top of Memory) represents upper boundary of on-chip program memory space (see Figure 6-1 for device-specific
values). Shaded areas represent unimplemented, or inaccessible areas, depending on the mode.
Note 1: This mode is the only available mode on 64-pin devices and the default mode on 80-pin devices.
2: These modes are only available on 80-pin devices.
3: Addresses starting at the top of the program memory are translated to start at 0000h of the external device whenever
the EASHFT Configuration bit is set.
TABLE 6-2: MEMORY ACCESS FOR PIC18F8X11/8616 PROGRAM MEMORY MODES
Internal Program Memory
External Program Memory
Operating Mode
Execution Table Read Table Write Execution Table Read Table Write
From
From
To
From
From
To
Microcontroller
Yes
Yes
Yes
No Access No Access No Access
Extended Microcontroller
Yes
Yes
Yes
Yes
Yes
Yes
DS39778E-page 70
 2007-2012 Microchip Technology Inc.