Am79C965A
35
PIN DESCRIPTION: 486 LOCAL
BUS MODE
Configuration Pins
JTAGSEL
JTAG Function Select
The value of this pin will asynchronously select
between JTAG Mode and Multi-Interrupt Mode.
Input
The value of this pin will asynchronously affect the
function of the JTAG
–
INTR
–
Daisy chain arbitration
pins, regardless of the state of the RESET pin and
regardless of the state of the BCLK pin. If the value is
a
“
1
”
, then the PCnet-32 controller will be programmed
for JTAG mode. If the value is a
“
0
”
, then the PCnet-32
controller will be programmed for Multi-Interrupt Mode.
When programmed for JTAG mode, four pins of the
PCnet-32 controller will be configured as a JTAG (IEEE
1149.1) Test Access Port. When programmed for Multi-
Interrupt Mode, two of the JTAG pins will become
interrupts and two JTAG pins will be used for daisy
chain arbitration support. Table 11 below outlines the
pin changes that will occur by programming the
JTAGSEL pin.
Table 11. JTAG Pin Changes
The JTAGSEL pin may be tied directly to
V
DD
or
V
SS
.
A
series resistor may be used but is not necessary.
LB/VESA
Local Bus/VESA VL-Bus Select
The value of this pin will asynchronously determine the
operating mode of the PCnet-32 controller, regardless
of the state of RESET and regardless of the state of the
BCLK pin. If the
LB
/
VESA
pin is tied to
V
DD
, then the
PCnet-32 controller will be programmed for Local Bus
Mode. If the
LB
/
VESA
pin is tied to
V
SS
, then the
PCnet-32
controller will be programmed for VESA VL-Bus Mode.
Input
Note that the setting of LB/VESA determines the func-
tionality of the following pins (names in parentheses
are pins in the VESA VL-Bus Mode): Am486 (VLBEN),
RESET (RESET), AHOLD (LBS16), HOLD (LREQ),
HLDA(LGNT), HOLDI (LREQI), and HLDAO (LGNTO).
Am486
Am486 Mode Select
The Am486 pin should be tied directly to
V
SS
. A series
resistor may be used but is not necessary.
Input
Note:
This pin is used to enable bursing in the VESA
VL-Bus mode when the LB/VESA pin has been tied to
VSS. See the pin description for the VLBEN pin in the
VESA VL-Bus Mode section.
Configuration Pin Settings Summary
Table 12 shows the possible pin configurations that
may be invoked with the PCnet-32 controller
configuration pins.
Table 12. Configuration Pin Settings
*X = Don
’
t care
Pin
JTAGSEL=1
JTAG Mode
JTAGSEL=0
Multi-Interrupt Mode
HLDAO/TCK
TCK
HLDAO
HOLDI/TDO
TDO
HOLDI
INTR3/TDI
TDI
INTR3
INTR4/TMS
TMS
INTR4
LB/VESA
Am486/Am386
JTAGSEL
Mode Selected
0
X*
0
VL Bus mode with 4 interrupts and daisy chain arbitration
0
X*
1
VL Bus mode with 2 interrupts and JTAG
1
0
0
Am486 mode with 4 interrupts and daisy chain arbitration
1
0
1
Am486 mode with 2 interrupts and JTAG
1
1
X
Reserved