External Signals
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
12-43
Some other input signals do not require a pull-up resistor, as they may be actively driven by external logic.
However, if they are not used externally, or if the external logic connected to them is not always actively
driving, they may need external pull-up resistors to keep them negated. These signals include the
following:
•
PORESET
•
AS
•
CR/IRQ3
•
KR/RETRY/IRQ4/SPKROUT (if configured as KR/RETRY or IRQ4)
•
Any IRQx (if configured as IRQx)
•
BR (if the internal bus arbiter is used)
•
BG (if an external bus arbiter is used)
12.6.2
JTAG and Debug Ports
Recommendations on configuration of the JTAG pins (including TMS, TRST, TDI, TDO, and TCK) are
made in
Section 54.6, “Recommended TAP Configuration.”
See also
Section 11.4, “TRST
Considerations.”
TCK/DSCK or ALE_B/DSCK/AT1 (depending on the configuration of the DSCK function) should be
connected to ground through a pull-down resistor to disable debug mode as a default. When required, an
external debug-mode controller can actively drive this signal high to put the processor into debug mode.
The two signals TCK/DSCK and TDI/DSDI have special requirements to keep them from oscillating when
unused (see
Section 12.5, “Internal Pull-Up and Pull-Down Resistors”
).
12.6.3
Unused Inputs
In general, pull-up resistors should be used on any unused inputs to keep them from oscillating. For
example, if PCMCIA is not used, the PCMCIA input pins (WAIT_A, WAIT_B, IP_A[0:8], IP_B[0:8])
should have external pull-up resistors. However, unused pins of port A, B, C, or D can be configured as
outputs, and, if they are configured as outputs they do not require external terminations.
12.6.4
Unused Outputs
Unused outputs can be left unterminated.
Summary of Contents for PowerQUICC MPC870
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Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
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Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Page 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...