Freescale Semiconductor
11-1
MCF51CN128 Reference Manual, Rev. 6
Chapter 11
Mini-FlexBus
11.1
Introduction
This chapter describes external bus data transfer operations and error conditions. It describes transfers
initiated by the ColdFire processor (or any other bus master) and includes detailed timing diagrams
showing the interaction of signals in supported bus operations.
The Mini-FlexBus is a subset of the FlexBus module found on other ColdFire microprocessors. The
Mini-FlexBus minimizes package pin-outs while maintaining a high level of configurability and
functionality.
NOTE
•
In this chapter, unless otherwise noted, clock refers to the FB_CLK used
for the external bus (f
sys
).
•
Use pin mux control registers from
Section 2.3, “Pin Mux Controls
” to
assign Mini-FlexBus signals to the MCF51CN128 package pins.
•
Most pin functions default to GPIO and must be software configured
before using Mini-FlexBus.
11.1.1
Overview
A multi-function external bus interface called the Mini-FlexBus interface controller is provided on the
device with basic functionality of interfacing to slave-only devices. It can be directly connected to the
following asynchronous or synchronous devices with little or no additional circuitry:
•
External ROMs
•
Flash memories
•
Programmable logic devices
•
Other simple target (slave) devices
For asynchronous devices, a simple chip-select based interface can be used.
The Mini-FlexBus interface has up to two general purpose chip-selects, FB_CS[1:0]. The actual number
of chip selects available depends upon the device and its pin configuration.
