Chapter 8. Signal Descriptions
8-45
Non-Protocol Signal Descriptions
State Meaning
AssertedInitiates a complete hard reset operation when this input
transitions from negated to asserted. Causes a reset exception as
described in Section 4.6.1, òSystem Reset Exception (0x00100).ó
Output drivers are released to high impedance within Tve clocks
after the assertion of HRESET.
NegatedIndicates that normal operation should proceed. See
Section 9.7.3, òReset Inputs.ó
Timing Comments
AssertionMay occur at any time and may be asserted
asynchronously to the MPC7400 input clock; must be held asserted
for a minimum of 255 clock cycles after the PLL lock time has been
met. Refer to the MPC7400 hardware specification for further timing
comments.
NegationMay occur any time after the minimum reset pulse width
has been met.
This input has additional functionality in certain test modes.
8.5.3.5 Checkstop Input (CKSTP_IN)Input
Following are the state meaning and timing comments for the CKSTP_IN signal.
State Meaning
AssertedIndicates that the MPC7400 must terminate operation by
internally gating off all clocks, and release all outputs (except
CKSTP_OUT, L2CE, L2WE, and L2CLK_OUTx) to the
high-impedance state. Once CKSTP_IN has been asserted; it must
remain asserted until the system has been reset.
NegatedIndicates that normal operation should proceed. See
Section 9.7.2, òCheckstops.ó
Timing Comments
AssertionMay occur at any time and may be asserted
asynchronously to the input clocks.
NegationMay occur any time after the CKSTP_OUT output signal
has been asserted.
8.5.3.6 Checkstop Output (CKSTP_OUT)Output
Note that the CKSTP_OUT signal is an open-drain type output, and requires an external
pull-up resistor (for example, 10 k
W
to V
DD
) to assure proper negation of the CKSTP_OUT
signal. Following are the state meaning and timing comments for the CKSTP_OUT signal.
State Meaning
AssertedIndicates that the MPC7400 has detected a checkstop
condition and has ceased operation.
NegatedIndicates that the MPC7400 is operating normally.
See Section 9.7.2, òCheckstops.ó