MC68HC16Z1CPV16 Datasheet, PDF (175/500 Pages) Freescale Semiconductor, Inc – Symbols and Operators, CPU16 Register Mnemonics

Freescale Semiconductor, Inc.
4. Set the BYTE field to lower byte when using a 16-bit port, as the external vector
for a 16-bit port is fetched from the lower byte. Set the BYTE field to upper byte
when using an 8-bit port.
If an interrupting device does not provide a vector number, an autovector acknowledge
must be generated, either by asserting the AVEC pin or by generating AVEC internally
using the chip-select option register. This terminates the bus cycle.
5.9.4 Chip-Select Reset Operation
The least significant bit of each of the 2-bit chip-select pin assignment fields in
CSPAR0 and CSPAR1 each have a reset value of one. The reset values of the most
significant bits of each field are determined by the states of DATA[7:1] during reset.
There are weak internal pull-up drivers for each of the data lines so that chip-select
operation is selected by default out of reset. However, the internal pull-up drivers can
be overcome by bus loading effects.
To ensure a particular configuration out of reset, use an active device to put the data
lines in a known state during reset. The base address fields in chip-select base ad-
dress registers CSBAR[0:10] and chip-select option registers CSOR[0:10] have the re-
set values shown in Table 5-25. The BYTE fields of CSOR[0:10] have a reset value of
“disable”, so that a chip-select signal cannot be asserted until the base and option reg-
isters are initialized.
Table 5-25 Chip-Select Base and Option Register Reset Values
Fields
Base address
Block size
Async/sync mode
Upper/lower byte
Read/write
AS/DS
DSACK
Address space
IPL
Autovector
Reset Values
$000000
2 Kbyte
Asynchronous mode
Disabled
Disabled
AS
No wait states
CPU space
Any level
External interrupt vector
Following reset, the MCU fetches the initial stack pointer and program counter values
from the exception vector table, beginning at $000000 in supervisor program space.
The CSBOOT chip-select signal is used to select an external boot device mapped to
a base address of $000000.
The MSB of the CSBTPA field in CSPAR0 has a reset value of one, so that chip-select
function is selected by default out of reset. The BYTE field in chip-select option register
CSORBT has a reset value of “both bytes” so that the select signal is enabled out of
reset. The LSB of the CSBOOT field, determined by the logic level of DATA0 during
reset, selects the boot ROM port size. When DATA0 is held low during reset, port size
is eight bits. When DATA0 is held high during reset, port size is 16 bits. DATA0 has a
weak internal pull-up driver, so that a 16-bit port is selected by default
M68HC16 Z SERIES
USER’S MANUAL
SYSTEM INTEGRATION MODULE
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