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MPC555
/
MPC556
SIGNAL DESCRIPTIONS
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
2-17
2.3.1.21 WE[0:3]
/
BE[0:3]/AT[0:3]
Pin Name:
we_b_at[0:3](4 pins)
Write Enable[0:3]/Byte Enable[0:3] –
This output line is asserted when a write ac-
cess to an external slave controlled by the GPCM in the memory controller is initiated
by the chip. It can be optionally be asserted on all read and write accesses. See WEBS
bit definition in
. WE[0]
/
BE[0] is asserted if the data lane DATA[0:7] contains
valid data to be stored by the slave device. WE[1]/BE[1] is asserted if the data lane
DATA[8:15] contains valid data to be stored by the slave device. WE[2]/BE[2] is as-
serted if the data line DATA[16:23] contains valid data to be stored by the slave device.
WE[3]/BE[3] is asserted if the data lane DATA[24:31] contains valid data to be stored
by the slave device.
Address Type –
Indicates one of the 16 address types to which the address applies.
The address type signals are valid at the rising edge of the clock in which the Special
Transfer Start (STS) is asserted.
2.3.1.22 PORESET
Pin Name
: poreset_b
Power on Reset –
This pin should be activated as a result of a voltage failure on the
keep-alive power pins. The pin has a glitch detector to ensure that low spikes of less
than 20 ns are rejected. The internal PORESET signal is asserted only if PORESET
is asserted for more than 100 ns. See
for more details on timing.
2.3.1.23 HRESET
Pin Name
: hreset_b
Hard Reset –
The chip can detect an external assertion of HRESET only if it occurs
while the chip is not asserting reset. After negation of HRESET or SRESET is detect-
ed, a 16 cycles period is taken before testing the presence of an external reset. The
internal HRESET signal is asserted only if HRESET is asserted for more than 100 ns.
To meet external timing requirements, an external pull-up device is required to negate
HRESET. See
for more details on timing.
2.3.1.24 SRESET
Pin Name
: sreset_b
Soft Reset –
The chip can detect an external assertion of SRESET only if it occurs
while the chip is not asserting reset. After negation of HRESET or SRESET is detect-
ed, a 16-cycle period is taken before testing the presence of an external soft reset. To
meet external timing requirements, an external pull-up device is required to negate
SRESET. See
for more details on timing.
2.3.1.25 SGPIOC[6]/FRZ/PTR
Pin Name
: sgpioc6_frz_ptr_b
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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