© 2008 Microchip Technology Inc. DS01210A-page 1
AN1210
INTRODUCTION
This application note describes the methodology to use
the Parallel Master Port (PMP) module to interface with
external data memory; either external Flash or external
RAM. This application note also lists the APIs and
describes how to implement different types of
interfaces.
Using the PMP module, the memory devices with
64K locations (Kbytes or K words) can be interfaced
with no extra I/Os and software. This application note
describes how to interface the memory devices with
more than 64K locations using some I/O pins and
provides the required APIs.
This application note describes the following topics:
• “External Data Memory Interface Overview”
• “Functional Implementation”
• “Expansion Of External Memory”
• “Reference Code”
EXTERNAL DATA MEMORY
INTERFACE OVERVIEW
The PIC24F/24H/dsPIC33F architecture supports up to
64 Kbytes of internal data memory. If internal memory
is insufficient, the external memory can be used. But,
this external memory cannot be directly accessed by
the CPU of the controller. The CPU can access through
the PMP module.
This section describes the topics:
• Signals Required for Interfacing Memory Devices
• Signals Generated by the PMP Module
• Registers Associated with the PMP Module
Signals Required for Interfacing Memory
Devices
Table 1 provides the signals required to interface
different types of memory devices.
TABLE 1: TYPICAL MEMORY DEVICE
INTERFACE CONNECTIONS
Author: Vidyadhar Vivekananda
Microchip Technology Inc.
Pin Name Function
Address Lines
(A0toAn)
‘n’ number of lines are
required to address all the
memory locations in a
2
n
Kbytes/K words memory
device.
Data Lines
(I/O 0 to 7 or I/O 0 to
15)
8 or 16 Data Lines are
required to read/write the
data in a byte or word
memory device.
Chip Enable
(CE
)
One Chip Enable signal for
each memory device.
Write Enable
(WE
)
One Write Enable signal,
which should go active
whenever data is to be
written into the memory
device.
Output Enable
(OE
)
One Output Enable signal,
which should go active
whenever data is to be read
from the memory device.
Byte Enable (A-1) and
Word/Byte
One Byte Enable signal and
one Word/Byte
signal, if the
memory device is a 16-bit
device and supports both
Word and Byte modes.
Using External Data Memory with
PIC24F/24H/dsPIC33F Devices
