mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 170

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

5-62
MOTOROLA
Chip-select assertion can be synchronized with bus control signals to provide output
enable, read/write strobe, or interrupt acknowledge signals. Logic can also generate
DSACK and AVEC signals internally. A single DSACK generator is shared by all chip-
selects. Each signal can also be synchronized with the ECLK signal available on
ADDR23.
When a memory access occurs, chip-select logic compares address space type,
address, type of access, transfer size, and interrupt priority (in the case of interrupt
acknowledge) to parameters stored in chip-select registers. If all parameters match,
the appropriate chip-select signal is asserted. Select signals are active low. If a chip-
select function is given the same address as a microcontroller module or an internal
memory array, an access to that address goes to the module or array, and the chip-
select signal is not asserted. The external address and data buses do not reflect the
internal access.
All chip-select circuits are configured for operation out of reset. However, all chip-
select signals except CSBOOT are disabled, and cannot be asserted until the
BYTE[1:0] field in the corresponding option register is programmed to a non-zero val-
ue to select a transfer size. The chip-select option register must not be written until a
base address has been written to a proper base address register. Alternate functions
for chip-select pins are enabled if appropriate data bus pins are held low at the release
of RESET. Refer to 5.7.3.2 Data Bus Mode Selection for more information. Figure 5-
21 is a functional diagram of a single chip-select circuit.
DSACK
BUS CONTROL
AVEC
ADDRESS
INTERNAL
SIGNALS
Figure 5-21 Chip-Select Circuit Block Diagram
Freescale Semiconductor, Inc.
GENERATOR
For More Information On This Product,
AVEC
BASE ADDRESS REGISTER
ADDRESS COMPARATOR
OPTION COMPARE
OPTION REGISTER
Go to: www.freescale.com
GENERATOR
DSACK
ASSIGNMENT
REGISTER
PIN
CONTROL
TIMING
AND
REGISTER
DATA
PIN
MC68HC16Y3/916Y3
USER’S MANUAL
PIN
CHIP SEL BLOCK