MPC555
/
MPC556
QUEUED SERIAL MULTI-CHANNEL MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
14-22
Figure 14-5 QSPI RAM
14.7.2.1 Receive RAM
Data received by the QSPI is stored in this segment, to be read by the CPU. Data
stored in the receive RAM is right-justified,( i.e., the least significant bit is always in the
right-most bit position within the word regardless of the serial transfer length). Unused
bits in a receive queue entry are set to zero by the QSPI upon completion of the indi-
vidual queue entry. The CPU can access the data using byte, half-word, or word ad-
dressing.
The CPTQP value in SPSR shows which queue entries have been executed. The CPU
uses this information to determine which locations in receive RAM contain valid data
before reading them.
14.7.2.2 Transmit RAM
Data that is to be transmitted by the QSPI is stored in this segment. The CPU normally
writes one word of data into this segment for each queue command to be executed. If
the corresponding peripheral, such as a serial input port, is used solely to input data,
then this segment does not need to be initialized.
Data must be written to transmit RAM in a right-justified format. The QSPI cannot mod-
ify information in the transmit RAM. The QSPI copies the information to its data serial-
izer for transmission. Information remains in transmit RAM until overwritten.
14.7.2.3 Command RAM
Command RAM is used by the QSPI in master mode. The CPU writes one byte of con-
trol information to this segment for each QSPI command to be executed. The QSPI
cannot modify information in command RAM.
Command RAM consists of 32 bytes. Each byte is divided into two fields. The periph-
eral chip-select field, enables peripherals for transfer. The command control field pro-
vides transfer options.
Receive
RAM
Transmit
RAM
0x30 5140
0x30 517F
0x30 5180
0x30 51BF
Half-Word
0x30 51C0
0x30 51DF
Command
RAM
Byte
Half-Word
RR0
RR1
RR2
RRD
RRE
RRF
TR0
TR1
TR2
TRD
TRE
TRF
CR0
CR1
CR2
CRD
CRE
CRF
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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