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CHAPTER 2 PIN FUNCTIONS
35
(2/3)
Symbol
Pin No.
I/O
I/O level
Function
STOP_B
27
I/O
Sustained
3-state
PCI
Stop
The STOP_B signal goes low when the target device
requests that the master device stop the current
transaction.
Device Select
When the
μ
PD98405 operates as the target and
recognizes an address after the FRAME_B signal has
been activated, it drives the DEVSEL_B signal low.
When the
μ
PD98405 operates as the master, it samples
the DEVSEL_B signal to check that the target device
has been selected.
Initial Device Select
A high level is input as the IDSEL signal when the
configuration register of the
μ
PD98405 is read or
written.
Request
The
μ
PD98405 drives the REQ_B signal low to request
bus mastership from the bus arbiter.
Grant
When the GNT_B signal is low, it indicates that the bus
arbiter has granted bus mastership to the
μ
PD98405.
Parity Error
The PERR_B signal is used to indicate that the
μ
PD98405 has detected a data parity error. When the
Parity Error Response bit of the configuration register is
set to 1, this pin is enabled.
System Error
The SERR_B signal is used to indicate that the
μ
PD98405 has detected an address parity error. When
both the Parity Error Response and System Error
Enable bits of the configuration register are set to 1, this
pin is enabled.
Interrupt Output
INTR_B is an open-drain pin to which a pull-up resistor
must be connected. INTR_B is used to inform the CPU
that an (unmasked) interrupt bit was set in the GSR.
Clock
CLK is the system bus clock input pin. The maximum
clock rate is 33 MHz.
DEVSEL_B
24
I/O
Sustained
3-state
PCI
IDSEL
5
I
PCI
REQ_B
294
O
Note
PCI
GNT_B
291
I
PCI
PERR_B
28
I/O
Sustained
3-state
PCI
SERR_B
29
O
N-ch
open-drain
INTR_B
288
O
N-ch
open-drain
CLK
290
I
PCI
Note
"PCI Local Bus Specification Revision 2.1" specifies that, while a low-level signal is being input to the
RST_B pin, the REQ_B pin must be set to high impedance. With the
μ
PD98405, however, the REQ_B
pin outputs a high level signal.