14-6
MCF5272 User’s Manual
Operation
14.4.1.2 Transmit RAM
Data to be transmitted by the QSPI is stored in the transmit RAM segment located at
addresses 0x0 to 0xF. The user normally writes 1 word into this segment for each queue
command to be executed. The user cannot read transmit RAM.
Out-bound data must be written to transmit RAM in a right-justified format. The unused
bits are ignored. The QSPI copies the data to its data serializer (shift register) for
transmission. The data is transmitted most significant bit first and remains in transmit RAM
until overwritten by the user.
14.4.1.3 Command RAM
The CPU writes one byte of control information to this segment for each QSPI command
to be executed. Command RAM is write-only memory from a user’s perspective.
Command RAM consists of 16 bytes with each byte divided into two fields. The peripheral
chip select field controls the QSPI_CS signal levels for the transfer. The command control
field provides transfer options.
A maximum of 16 commands can be in the queue. Queue execution proceeds from the
address in QWR[NEWQP] through the address in QWR[ENDQP].
The QSPI executes a queue of commands defined by the control bits in each command
RAM entry which sequence the following actions:
•
chip-select pins are activated
•
data is transmitted from transmit RAM and received into the receive RAM
•
the synchronous transfer clock QSPI_CLK is generated
Before any data transfers begin, control data must be written to the command RAM, and
any out-bound data must be written to transmit RAM. Also, the queue pointers must be
initialized to the first and last entries in the command queue.
Data transfer is synchronized with the internally generated QSPI_CLK, whose phase and
polarity are controlled by QMR[CPHA] and QMR[CPOL]. These control bits determine
which QSPI_CLK edge is used to drive outgoing data and to latch incoming data.
14.4.2 Baud Rate Selection
Baud rate is selected by writing a value from 1–255 into QMR[BAUD]. The QSPI uses a
prescaler to derive the QSPI_CLK rate from the system clock, CLKIN, divided by two.
A baud rate value of zero turns off the QSPI_CLK.
The desired QSPI_CLK baud rate is related to CLKIN and QMR[BAUD] by the following
expression:
QMR[BAUD] = CLKIN / [2
×
(desired QSPI_CLK baud rate)]
Summary of Contents for DigitalDNA ColdFire MCF5272
Page 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Page 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Page 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Page 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Page 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Page 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Page 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Page 338: ...13 44 MCF5272 User s Manual Application Examples ...
Page 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Page 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Page 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Page 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...