MC68332ACEH16 Datasheet, PDF (78/88 Pages) Freescale Semiconductor, Inc – 32-Bit Modular Microcontroller

Freescale Semiconductor, Inc.
Command RAM is used by the QSPI when in master mode. The CPU writes one byte of control infor-
mation to this segment for each QSPI command to be executed. The QSPI cannot modify information
in command RAM.
Command RAM consists of 16 bytes. Each byte is divided into two fields. The peripheral chip-select
field enables peripherals for transfer. The command control field provides transfer options.
A maximum of 16 commands can be in the queue. Queue execution by the QSPI proceeds from the
address in NEWQP through the address in ENDQP. (Both of these fields are in SPCR2.)
CONT — Continue
0 = Control of chip selects returned to PORTQS after transfer is complete.
1 = Peripheral chip selects remain asserted after transfer is complete.
BITSE — Bits per Transfer Enable
0 = 8 bits
1 = Number of bits set in BITS field of SPCR0
DT — Delay after Transfer
The QSPI provides a variable delay at the end of serial transfer to facilitate the interface with peripherals
that have a latency requirement. The delay between transfers is determined by the SPCR1 DTL field.
DSCK — PCS to SCK Delay
0 = PCS valid to SCK transition is one-half SCK.
1 = SPCR1 DSCKL field specifies delay from PCS valid to SCK.
PCS[3:0] — Peripheral Chip Select
Use peripheral chip-select bits to select an external device for serial data transfer. More than one pe-
ripheral chip select can be activated at a time, and more than one peripheral chip can be connected to
each PCS pin, provided that proper fanout is observed.
SS — Slave Mode Select
Initiates slave mode serial transfer. If SS is taken low when the QSPI is in master mode, a mode fault
will be generated.
6.5.4 Operating Modes
The QSPI operates in either master or slave mode. Master mode is used when the MCU originates data
transfers. Slave mode is used when an external device initiates serial transfers to the MCU through the
QSPI. Switching between the modes is controlled by MSTR in SPCR0. Before entering either mode,
appropriate QSM and QSPI registers must be properly initialized.
In master mode, the QSPI executes a queue of commands defined by control bits in each command
RAM queue entry. Chip-select pins are activated, data is transmitted from transmit RAM and received
into receive RAM.
In slave mode, operation proceeds in response to SS pin activation by an external bus master. Opera-
tion is similar to master mode, but no peripheral chip selects are generated, and the number of bits
transferred is controlled in a different manner. When the QSPI is selected, it automatically executes the
next queue transfer to exchange data with the external device correctly.
Although the QSPI inherently supports multimaster operation, no special arbitration mechanism is pro-
vided. A mode fault flag (MODF) indicates a request for SPI master arbitration. System software must
provide arbitration. Note that unlike previous SPI systems, MSTR is not cleared by a mode fault being
set, nor are the QSPI pin output drivers disabled. The QSPI and associated output drivers must be dis-
abled by clearing SPE in SPCR1.
MOTOROLA
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