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CHAPTER 4 INTERFACES
85
(5) Target termination
When the
μ
PD98405 operates as the target, it may execute retry, disconnect, or target abort processing to
request the termination of the transaction.
a)
Retry
The host system issues a command to the EECR register of the
μ
PD98405 to access an external
EEPROM. The
μ
PD98405 cannot accept such a command successively because a fixed time is
required for the
μ
PD98405 to access the external EEPROM. Therefore, when the EECR register is
accessed successively, the
μ
PD98405 requests a retry.
If the command FIFO is full when the host system attempts to issue a command, the
μ
PD98405 request
a retry.
b)
Disconnect
When a
μ
PD98405 internal register (direct address register or configuration register) is accessed by
performing burst transfer, the
μ
PD98405 activates STOP_B to disconnect the transaction when 1-word
transfer terminates.
When an external expansion ROM or external EEPROM is accessed by performing burst transfer, the
μ
PD98405 disconnects the transaction.
c)
Target abort
When the
μ
PD98405 receives an address and detects a parity error in it, it performs target abort
processing.
When PCBE3_B through PCBE0_B for a data transaction are not all 0, the
μ
PD98405 performs target
abort processing.
4.2.5 Burst Size
(1) Normal burst
The
μ
PD98405 normally reads/writes cell data by performing 12-word burst DMA transfer. (When multi-cell
transfer is enabled, the
μ
PD98405 performs burst transfer for several cells. See
Section 4.2.5 (2)
.) 12-
word burst means 1-cell burst transfer. When the transmit data or receive buffer is shorter than 12 words,
the
μ
PD98405 performs burst transfer of the corresponding size. The following table lists the burst sizes
for other than cell data.