
Signal Descriptions
SYM53C810A Data Manual
4-7
Table 4-8: Additional Interface Pins
Symbol
Pin No.
Type
Description
T EST IN/
52
I
Test In
. When this pin is driven low, the SYM53C810A connects all
inputs and outputs to an “AND tree.” T he SCSI control signals
and data lines are not connected to the “AND tree.” T he output of
the “AND tree” is connected to the Test Out pin. T his allows man-
ufacturers to verify chip connectivity and determine exactly which
pins are not properly attached. When the T EST IN pin is driven
low, internal pull-ups are enabled on all input, output, and bidirec-
tional pins, all outputs and bidirectional signals will be tri-stated,
and the MAC/_T EST OUT pin will be enabled. Connectivity can
be tested by driving one of the SYM53C810A pins low. T he MAC/
_T EST OUT pin should respond by also driving low.
General Purpose I/O
pin
.
Optionally, when driven low, indicates that
the next bus request will be for an op code fetch. T his pin powers
up as a general purpose input.
T his pin has two specific purposes in the Symbios Logic SDMS
software. SDMS uses it to toggle SCSI device LEDs, turning on
the LED whenever the SYM53C810A is on the SCSI bus. SDMS
drives this pin low to turn on the LED, or drives it high to turn off
the LED. T his signal can also be used as data I/O for serial
EEPROM access. In this case it is used with the GPIO0 pin, which
serves as a clock. T he pin can be controlled from PCI configuration
register 35h or observed from the GPREG operating register, at
address 07h.
General Purpose I/O
pin. Optionally, when driven low, indicates that
the SYM53C810A is bus master. T his pin powers up as a general
purpose input.
Symbios Logic SDMS software supports use of this signal in serial
EPROM applications, when enabled, in combination with the
GPIO0 pin. When this signal is used as a clock for serial EEPROM
access, the GPIO1 pin serves as data, and the pin is controlled
from PCI configuration register 35h.
Memory Access Control/Test Out
. T his pin can be programmed to
indicate local or system memory accesses (non-PCI applications).
It is also used to test the connectivity of the SYM53C810A signals
using an “AND tree” scheme. T he MAC/_T EST OUT pin is only
driven as the Test Out function when the T EST IN/ pin is driven
low.
Interrupt
. T his signal, when asserted low, indicates that an inter-
rupting condition has occurred and that service is required from
the host CPU. T he output drive of this pin is programmed as either
open drain with an internal weak pull-up or, optionally, as a totem
pole driver. Refer to the description of DCNT L Register, bit 3, for
additional information.
GPIO0_
FET CH/
48
I/O
GPIO1_
MAST ER/
49
I/O
MAC_
T EST OUT
53
T /S
IRQ/
47
O