mc68336 Freescale Semiconductor, Inc, mc68336 Datasheet - Page 6

• Manufacturer Part Number: mc68336
• Description: An Introduction To The Mc68331 And Mc68332
• Manufacturer: Freescale Semiconductor, Inc

2.4 Using Sockets
Because of the high pin count the MCU package has a very narrow lead pitch, which makes it nearly im-
possible to hand-solder onto a board. This is not a problem for design activities that can manufacture PC
boards, but designers who are assembling a limited number of prototypes or who cannot manufacture PC
boards will probably need to use a socket to hold the chip.The wider spacing of socket pins makes it possi-
ble to connect the socket to a board.
Sockets are not a place to economize. Use a good quality socket that firmly holds the MCU in place so that
all pins maintain contact. If the MCU is likely to be removed and replaced, consider using a zero insertion
force socket.
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2. Hold DATA9 high during reset as described in 2.1 Using Data Bus Pins to Configure the MCU to
Remember that the level seven interrupt is non-maskable — when configured as an interrupt line, IRQ7
is always enabled. The only way to disable external IRQ7 interrupts is to assign the IRQ7 pin to I/O func-
tion via the port F pin assignment register.
DSACK[1:0] — During bus transfers, external devices can drive these signals to indicate port width.
These signals are active even if the bus transfer is to or from a peripheral that is using one of the chip-
selects to terminate the bus cycle. Putting 10 K pull-ups on these two pins prevents accidental asser-
tion of DSACK[1:0], which can occur if the pins are left floating.
AVEC — If this signal is asserted during an interrupt acknowledge cycle, an autovector will be used for
the external interrupt being serviced. If the AVEC pin is connected permanently to ground, all external
interrupts will autovector. Using a 10 K pull-up resistor will prevent unexpected assertion of the AVEC
pin.
TSTME/TSC — The inactive state of this pin is five volts. Pulling it low enables special test mode, but
the MCU cannot enter test mode unless the state of a bit in one of the test mode registers is changed
by the software. Although this should happen only if the software is corrupted, to prevent entering spe-
cial test mode, put a 10 K pull-up resistor on this pin. Special test mode is generally used only for fac-
tory testing, although there are certain circumstances, such as debugging TPU microcode, in which a
limited subset of test mode capabilities are available to users. Driving this pin to approximately 1.6 times
V
rest of the system.
BKPT/DSCLK — Background debug mode (BDM) operation is enabled when BKPT is asserted at the
rising edge of the RESET signal. BDM remains enabled until the next system reset. If BKPT is at a logic
level one on the trailing edge of RESET, BDM is disabled. BKPT is re-latched on each rising transition
of RESET. A 4.7 K pull-up resistor will ensure that BDM is not unexpectedly enabled upon reset.
R/W — Putting a 10 K
device is being powered up. Normally, R/W is always defined. However, when power is first applied to
the device, R/W can be undefined for a few cycles. This may cause a problem for EEPROM or battery
backed up RAM.
RESET — An 820
The reason for such a strong pull-up and no extra capacitance is that the RESET line must rise to a
logic one within approximately ten system clocks after the MCU has driven RESET low for 512 clocks,
or else the MCU must re-assert the RESET line for an additional 512 clock cycles.
MODCLK — If using the internal PLL to generate the system clock, this pin must be pulled up with a 10
K
nect this pin to ground or drive it low during reset.
DD
assign all these pins to use as interrupt-request inputs. Pull up all lines that are to be used for interrupt
service, including IRQ7, to five volts via 10 K resistors, hold DATA9 high during reset, reassign the
pins that are not used for interrupt requests by writing to the port F pin assignment register, then
change the IPL mask value to enable maskable interrupts.
resistor or driven high during reset. If using an external clock source and bypassing the PLL, con-
causes the MCU to place all output drivers in a high-impedance state, isolating the MCU from the
pull-up resistor is required for this pin. Do not put capacitors on the RESET pin.
Freescale Semiconductor, Inc.
pull-up resistor on this pin will prevent accidental writes to memory while the
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M68331/332TUT/D
MC68331/332