mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 150

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

5.7.3.1 Address and Data Bus Pin Functions
5-42
MOTOROLA
BERR, BKPT, and MODCLK do not have internal pull-ups and must be driven to the
desired state during reset.
When BERR is high during reset, the MCU is configured for partially or fully expanded
operation. DATA2 is then decoded to select 8- or 16-bit data bus operation, DATA8 is
decoded to configure pins for bus control or port E operation, and DATA9 is decoded
to configure pins for interrupt requests or port F operation. If DATA1 is held low at re-
set, selecting 16-bit data bus operation, DATA11, DATA[7:2] and DATA0 are also de-
coded. The following subsections explain the process in greater detail.
External bus configuration determines whether certain address and data pins are used
for those functions or for general-purpose I/O. ADDR[18:3] serve as pins for ports A
and B when the MCU is operating in single-chip mode. DATA[7:0] serve as port H pins
in partially expanded and single-chip modes, and DATA[15:8] serve as port G pins
during single-chip operation. Table 5-16 summarizes bus and port configuration op-
tions.
ADDR[2:0] are normally placed in a high-impedance state in single-chip mode and
function as normal address bus pins in the expanded modes. Refer to D.2.1 SCIM
Configuration Register for information on the address bus disable (ABD) bit.
The ADDR[23:19] pins can also be used as chip selects or discrete output pins, de-
pending on the external bus configuration selected at reset. The following paragraphs
contain a summary of pin configuration options for each external bus configuration.
16-Bit Expanded
8-Bit Expanded
DATA1 (if BERR = 1)
Single Chip
Mode
Select Pin
MODCLK
BERR
BKPT
Table 5-16 Bus and Port Configuration Options
Table 5-15 Basic Configuration Options
Freescale Semiconductor, Inc.
For More Information On This Product,
Address Bus
ADDR[18:3]
ADDR[18:3]
None
Go to: www.freescale.com
Background mode disabled
Synthesized system clock
8-Bit expanded mode
Default Function
Expanded mode
(Pin Left High)
DATA[15:0]
DATA[15:8]
Data Bus
None
Background mode enabled
16-Bit expanded mode
External system clock
Alternate Function
(Pin Pulled Low)
Single-chip mode
ADDR[18:11] = Port A
ADDR[10:3] = Port B
DATA[15:8] = Port G
DATA[7:0] = Port H
DATA[7:0] = Port H
I/O Ports
MC68HC16Y3/916Y3
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USER’S MANUAL