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CHAPTER 2 PIN FUNCTIONS
32
(3/4)
Symbol
Pin No.
I/O
I/O level
Function
ABRT_B
27
I
TTL
Abort
ABRT_B is used to abort a data transfer cycle. When this
signal is low during the data transfer cycle, the cycle is
aborted and the
μ
PD98405 will retry the burst starting from
the aborted data. Note that the RDY_B signal has no effect
if the ABRT_B signal is low. The timing at which the
μ
PD98405 samples the RDY_B and ABRT_B signals can be
changed to one clock earlier (early mode) by setting an
internal register (GMR). Connect a pull-up resistor when the
ABRT_B pin is not used.
System Bus Error
The ERR_B signal is used by the bus control device to
request the
μ
PD98405 to halt operation if an error is
detected on the system bus.
Once this signal has been set to low, the
μ
PD98405
immediately halts all bus operations, sets the system bus
error bit (bit 25) in the GSR (if not masked) to generate an
interrupt. Connect a pull-up resistor when this pin is not
used.
Slave Read/Write
The SR/W_B signal determines the direction of slave
access.
1:
Read access
0:
Write access
Slave Select
Set the SEL_B signal to active low when selecting the
μ
PD98405 as a slave. The SEL_B signal must be made low
either at the same time as when the ASEL_B signal goes
low, or subsequently. Once the SEL_B signal has been
inactive, it must be held inactive for at least two system clock
cycles before it can be active.
Slave Address Select
The ASEL_B signal is used to select the
μ
PD98405 directly
addressed registers.
When ASEL_B is low, the
μ
PD98405 samples the AD lines
at the first rising edge of CLK.
Clock
CLK is the system bus clock input pin. The clock rate is up
to 33 MHz.
Reset
The RST_B signal provides a means of initializing the
μ
PD98405 (i.e. at power on). After the completion of a reset,
the
μ
PD98405 can start normal operation. Once RST_B has
been set to low, it resets the
μ
PD98405 internal state
machines and registers, and forces all 3-state signals to the
high impedance state. Reset input is performed
asynchronously. If low during operation, current state will be
lost. RST_B should be kept low for at least one clock cycle.
ERR_B
28
I
TTL
SR/W_B
24
I
TTL
SEL_B
21
I
TTL
ASEL_B
22
I
TTL
CLK
290
I
TTL
RST_B
289
I
TTL