PIC18F6585 Datasheet, PDF (98/496 Pages) Microchip Technology – 64/68/80-Pin High-Performance, 64-Kbyte Enhanced Flash Microcontrollers with ECAN Module

PIC18F6585/8585/6680/8680
6.2 16-bit Mode
The external memory interface implemented in
PIC18F8X8X devices operates only in 16-bit mode.
The mode selection is not software configurable but is
programmed via the configuration bits.
The WM<1:0> bits in the MEMCON register determine
three types of connections in 16-bit mode. They are
referred to as:
• 16-bit Byte Write
• 16-bit Word Write
• 16-bit Byte Select
These three different configurations allow the designer
maximum flexibility in using 8-bit and 16-bit memory
devices.
For all 16-bit modes, the Address Latch Enable (ALE)
pin indicates that the Address bits (A<15:0>) are avail-
able on the external memory interface bus. Following
the address latch, the Output Enable signal (OE ) will
enable both bytes of program memory at once to form
a 16-bit instruction word.
In Byte Select mode, JEDEC standard Flash memories
will require BA0 for the byte address line, and one I/O
line to select between Byte and Word mode. The other
16-bit modes do not need BA0. JEDEC standard static
RAM memories will use the UB or LB signals for byte
selection.
6.2.1 16-BIT BYTE WRITE MODE
Figure 6-1 shows an example of 16-bit Byte Write
mode for PIC18F8X8X devices.
FIGURE 6-1:
16-BIT BYTE WRITE MODE EXAMPLE
D<7:0>
PIC18F8X8X
AD<7:0>
AD<15:8>
ALE
A<19:16>
CE
OE
WRH
WRL
373
A<19:0>
D<15:8>
373
(MSB)
A<x:0>
D<7:0>
CE
OE WR⁽¹⁾
(LSB)
A<x:0>
D<7:0>
D<7:0>
CE
OE WR⁽¹⁾
Address Bus
Data Bus
Control Lines
Note 1: This signal only applies to table writes. See Section 5.1 “Table Reads and Table Writes”.
DS30491C-page 96
 2004 Microchip Technology Inc.