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CHAPTER 5 SAR FUNCTION
236
Address
Name
Register name
Word address mode
Byte address mode
CMR
08H
20H
Command register
CMR_L
09H
24H
CER
0AH
28H
Command extension
register
CER_L
0BH
2CH
The
μ
PD98405 uses different registers depending on whether it is controlled by a single host CPU in a
single-host system or by two or more host CPUs in a multi-host system.
<1>
In a single-host system
When the host issues commands to the
μ
PD98405, only CMR and CER of the command and
command extension registers are effective. CMR_L and CER_L are not used.
<2>
In a multi-host system
When the host CPUs issue commands to the
μ
PD98405, all the command and command extension
registers, CMR, CMR_L, CER, and CER_L, are used.
(2) Commands returning command indication
When an Open_Channel or Close_Channel command is executed, the
μ
PD98405 stores a command
indication to the command register.
When the host has issued a command having a command indication, it reads the command register to
obtain the command indication. The
μ
PD98405 stores the command indication to the command register
upon the completion of command execution. The B bit being set to "1" indicates that the command has not
yet been completed, and that the command indication has not been stored to the command register. When
the B bit is set to "0," the command indication is stored to the command register. The host polls the
command register until the B bit is cleared to "0."
(3) Commands using command extension register
The Indirect_Access and Add_Batches commands use the command extension register because these
commands require that parameters be set.
When data is written, it is first written to the command extension register, after which a command is set to
the command register. As soon as the data has been written to the command register, the
μ
PD98405
executes the command. Consequently, the data in the command extension register must be changed
before the command register is written.