![](http://datasheet.mmic.net.cn/Freescale-Semiconductor/MC68F375MZP33R2_datasheet_98733/MC68F375MZP33R2_146.png)
MC68F375
SINGLE-CHIP INTEGRATION MODULE 2 (SCIM2E)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
4-64
Figure 4-20 Alternate Circuit for Data Bus Mode Select Conditioning
In the simpler of these two circuits, a resistor is connected in series with a diode from
the data bus pin to the RESET line. A bipolar transistor can be used for the same pur-
pose, but an additional current limiting resistor must be connected between the base
of the transistor and the RESET pin. If a MOSFET is substituted for the bipolar tran-
sistor, only the 1 K
isolation resistor is required.
4.7.8.3 Single-Chip Mode
When BERR = 0 at the release of RESET, single-chip operation is selected. BERR
must return to a logic 1 before the first bus cycle after reset to insure proper device
operation. The external bus interface is essentially disabled in single-chip mode, and
SCIM2E pins generally serve as discrete inputs and outputs. The behavior of specific
pin groups is discussed in the following paragraphs.
NOTE
The paragraphs that follow describe the behavior of SCIM2E pins in
single-chip mode only. Sections that follow cover 16-bit and 8-bit
expanded modes.
ADDR[2:0] have no discrete I/O function in single-chip mode. These pins are placed
in a high-impedance state at power-on but can be enabled by clearing the ABD bit in
SCIMMCR.
ADDR[18:11] become port A input/output pins PA[7:0], and ADDR[10:3] become port
B input/output pins PB[7:0]. Each port is configurable entirely as inputs or outputs on
a per port basis by the DDA and DDB bits in the port A/B data direction register
(DDRAB).
Special attention should be paid to chip-select pins in single-chip mode. While each
chip-select base address register and option register is active and may be pro-
grammed as desired, a match condition will not assert the corresponding pin. For this
reason, chip selects should be used expressly to provide autovector termination of
interrupt acknowledge cycles generated in response to assertion of the IRQ[7:1] pins.
RESET
DATA PIN
RESET
1N4148
2N3906
ALTERNATE DATA BUS CONDITION CIRCUIT
2 k
1 k
1 k
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.