mc68331cpv20b1 Freescale Semiconductor, Inc, mc68331cpv20b1 Datasheet - Page 80

• Manufacturer Part Number: mc68331cpv20b1
• Description: Mc68331 32 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

4
4.6.3.1 Data Bus Mode Selection
4-38
All data lines have weak internal pull-up drivers. When pins are held high by the inter-
nal drivers, the MCU uses a default operating configuration. However, specific lines
can be held low externally to achieve an alternate configuration.
Use an active device to hold data bus lines low. Data bus configuration logic must re-
lease the bus before the first bus cycle after reset to prevent conflict with external
memory devices. The first bus cycle occurs ten CLKOUT cycles after RESET is re-
leased. If external mode selection logic causes a conflict of this type, an isolation re-
sistor on the driven lines may be required. Figure 4-15 shows a recommended method
for conditioning the mode select signals.
Mode Select Pin
MODCLK
External bus loading can overcome the weak internal pull-up drivers
on data bus lines, and hold pins low during reset.
DATA11
DATA0
DATA1
DATA2
DATA3
DATA4
DATA5
DATA6
DATA7
DATA8
DATA9
BKPT
Freescale Semiconductor, Inc.
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Table 4-16 Reset Mode Selection
SYSTEM INTEGRATION MODULE
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Background Mode Disabled
VCO = System Clock
Test Mode Disabled
Default Function
CSBOOT 16-Bit
(Pin Left High)
AVEC, DS, AS,
DSACK[1:0],
MODCLK
CS[10:6]
IRQ[7:1]
CS[7:6]
CS[8:6]
CS[9:6]
SIZE
CS0
CS1
CS2
CS3
CS4
CS5
CS6
NOTE
Background Mode Enabled
EXTAL = System Clock
Alternate Function
Test Mode Enabled
(Pin Pulled Low)
CSBOOT 8-Bit
ADDR[20:19]
ADDR[21:19]
ADDR[22:19]
ADDR[23:19]
ADDR19
BGACK
PORTE
PORTF
FC0
FC1
FC2
BR
BG
USER’S MANUAL
MC68331