MSC8122VT8000 datasheet(42/48 Pages) FREESCALE

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MSC8122 Quad Digital Signal Processor Data Sheet, Rev. 15

Hardware Design Considerations

Freescale Semiconductor

Note:

The MSC8122 does not support DLL-enabled mode. For the following two clock schemes, ensure that the DLL is

disabled (that is, the DLLDIS bit in the Hard Reset Configuration Word is set).

•

If no system synchronization is required (for example, the design does not use SDRAM), you can use any of the

available clock modes.

•In the CLKIN synchronization mode, use the following connections:

— Connect the oscillator output through a buffer to CLKIN.

— Connect the CLKIN buffer output to the slave device (for example, SDRAM) making sure that the delay path

between the clock buffer to the MSC8122 and the SDRAM is equal (that is, has a skew less than 100 ps).

— Valid clock modes in this scheme are: 0, 7, 15, 19, 21, 23, 28, 29, 30, and 31.

•In CLKOUT synchronization mode (for 1.2 V devices), CLKOUT is the main clock to SDRAM. Use the following

connections:

— Connect the oscillator output through a buffer to CLKIN.

— Connect CLKOUT through a zero-delay buffer to the slave device (for example, SDRAM) using the following

guidelines:

–

The maximum delay between the slave and CLKOUT must not exceed 0.7 ns.

–

The maximum load on CLKOUT must not exceed 10 pF.

–

Use a zero-delay buffer with a jitter less than 0.3 ns.

— All clock modes are valid in this clock scheme.

Note:

See the Clock chapter in the MSC8122 Reference Manual for details.

•

If the 60x-compatible system bus is not used and SIUMCR[PBSE] is set, PPBS can be disconnected. Otherwise, it

should be pulled up.

•

The following signals: SWTE, DSISYNC, DSI64, MODCK[1–2], CNFGS, CHIPID[0–3], RSTCONF and BM[0–2] are

used to configure the MSC8122 and are sampled on the deassertion of the PORESET signal. Therefore, they should

be tied to GND or VDDH or through a pull-down or a pull-up resistor until the deassertion of the PORESET signal.

•

When they are used, INT_OUT (if SIUMCR[INTODC] is cleared), NMI_OUT, and IRQxx (if not full drive) signals must

be pulled up.

•

When the Ethernet controller is enabled and the SMII mode is selected, GPIO10 and GPIO14 must not be connected

externally to any signal line.

Note:

For details on configuration, see the MSC8122 User’s Guide and MSC8122 Reference Manual. For additional

information, refer to the MSC8122 Design Checklist (AN2787)..

3.4

External SDRAM Selection

The external bus speed implemented in a system determines the speed of the SDRAM used on that bus. However, because of

differences in timing characteristics among various SDRAM manufacturers, you may have use a faster speed rated SDRAM to

assure efficient data transfer across the bus. For example, for 166 MHz operation, you may have to use 183 or 200 MHz

SDRAM. Always perform a detailed timing analysis using the MSC8122 bus timing values and the manufacturer specifications

for the SDRAM to ensure correct operation within your system design. The output delay listed in SDRAM specifications is

usually given for a load of 30 pF. Scale the number to your specific board load using the typical scaling number provided by

the SDRAM manufacturer.

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