MAC7200 datasheet(432/976 Pages) FREESCALE

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FlexBus Application Usage

MAC7200 Microcontroller Family Reference Manual, Rev. 2

354

Freescale Semiconductor

configuring of the external bus. If software can positively assure that no external bus accesses will occur

during the configuration of the chip select(s), then this step is not necessary.

To summarize, a short example is presented. To boot from an external device, and enable three chip selects

on the external bus, you would perform the following steps:

1. Boot the device (either Power On Reset or assert the RESET pin)

2. The external bus (if available) will be in Global Chip Select Mode, with all external bus accesses

mapped to CS0. CS1 and CS2 will be unavailable.

3. If the device is in Expanded Mode, it will boot from the external bus, causing CS0 to be asserted,

and a READ access to appear on the external bus. The Port Size and Auto Acknowledge bits

(CSCR[7] and CSCR[8], respectively) are determined by the value of the PF3 and PF2 pins

(respectively) at Reset.

4. The boot code (from the external device) can now re-configure all of the chip-selects, including

CS0. CS0 should be re-configured in most cases, because the Global Chip Select mode provides

the most flexible (and hence slowest) access to external devices.

5. To configure CS1, program the CSAR1, CSCR1 and CSMR1 register, ensuring that the Valid bit

(CSMR1[0]) is set. Even though the Valid bit is set, CS1 will not become active until Global Chip

Select Mode is exited.

6. Configuring CS2 is similar to configuring CS1.

7. To configure CS0 and exit Global Chip Select Mode, program the CSAR0, CSCR1 and CSMR0

registers. Once the Valid bit (CSMR0[0]) bit is set, the FlexBus will exit Global Chip Select Mode,

and all three chip selects will be active with their programmed configuration. Therefore, the

CSMR0 register should be programmed last.

17.7.3

FlexBus speed

Note that, due to the increase in the number of wait states in Global Chip Select Mode between the

MAC71xx and MAC7200 family of devices, the MAC72xx device will run about 4x slower when booting

from the external bus. For this reason, the FlexBus registers should be programmed as early in the boot

process as possible in order to set the correct number of wait states.

17.7.4

How to use the external bus in Expanded Secured/Unsecured Mode

There is no PIM setup required to use the external bus in Expanded Mode. In this mode, the following pins

are automatically changed to Peripheral Mode and the FlexBus clock is automatically enabled:

•

PA0-PA15

•

PC0-PC15

•

PD0-PD2

•

PD5-PD15

MAC7200 Datasheet(PDF) 432 Page - Freescale Semiconductor, Inc

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