AN2866 Freescale Semiconductor / Motorola, AN2866 Datasheet - Page 5

• Manufacturer Part Number: AN2866
• Description: Migrating from the MC68332 to the ColdFire MCF523x
• Manufacturer: Freescale Semiconductor / Motorola

Device Feature
2
This section addresses differences between the MC68332 and the MCF523x, and highlights what the user
needs to consider when making this migration. The categories discussed in this section include electrical
characteristics, mechanical characteristics, on-chip modules, and memory maps.
2.1
The following sections discuss differences in electrical characteristics between the two devices, including
voltage conversion, driver strength/capacitive loading, frequency and performance, and operating in 16-bit
mode.
2.1.1
One important consideration in migrating from the MC68332 to the MCF523x is the difference in voltage.
The MC68332 is a 5V only device, while the MCF523x is a dual supply device—3.3V supply for I/Os and
1.5V supply for the core. In addition, the MCF523x I/Os are not 5V tolerant, so the memories and external
peripheral devices used in an existing MC68332 system might not be compatible with the MCF523x bus
without proper system design. Bulk memories are readily available in 3.3V, so finding replacements for
memory devices should not present a problem. If any external peripherals that are only available as 5V
devices are needed, then level shifters/buffers will be required to isolate the peripherals 5V I/Os from the
MCF523x. Refer to
peripherals from a 3.3V bus.
2.1.2
Another issue to take into consideration when migrating from the MC68332 to the MCF523x is the drive
capability of the parts. Whereas the majority of MC68332 specifications assume a capacitive load between
90-130pF on the pin, the MCF523x tolerates loading up to 25pF for low drive strength and 50pF for high
drive. In many systems, external buffers will be needed to reduce the loading on the MCF523x bus.
Figure 2
remain unbuffered.)
Freescale Semiconductor
32-bit DMA
Crypto
Timer
WDT
CAN
PITs
shows a possible buffering scheme that can be used to reduce loading. (Note: SDRAM should
Device Differences
Electrical Characteristics
Voltage Conversion
Driver Strength/Capacitive Loading
MC68332
—
—
—
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1
Table 1. MC68332 to MCF523x Migration Issue Summary (continued)
Figure 2
Migrating from the MC68332 to the ColdFire
2 FlexCAN
MCF5235
for an example of how buffers can be used to isolate 5V memories and
√
√
4
4
Device Implementation
1 FlexCAN
MCF5234
—
√
4
4
2 FlexCAN
MCF5233
—
√
4
4
1 FlexCAN
MCF5232
®
—
√
4
4
MCF523x, Rev. 1.0
Hardware
—
—
—
√
√
Impact
Code
√
√
√
√
√
Device Differences
Criticality
Migration
Low
Low
Low
Low
Low
Number
Page
19
20
15
14
21
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