Appendix B. Specifications
94
STD Bus Loading Characteristics
The unit load is a convenient method for specifying the input and output drive capability of STD bus
cards. With this method, one unit load is equal to one LSTTL load as follows:
•
Current for single input load:
20 µA
•
Current for single output drive:
400 µA
The unit load reflects current requirements at worst case conditions over the recommended supply
voltage and operating temperature ranges. An output drive of 60 unit loads drives 60 STD bus cards
having input ratings of one unit load. The "STD Bus Loading, P Connector" table includes load values
for STD-80 connections. The "STD Bus Loading, E Connector" table includes load values for STD 32
connections.
STD Bus Loading, P Connector
+5 VDC
GND
DCPDN*
D7/A13 [1]
D6/A22 [1]
D5/A21 [1]
D4/A20 [1]
A15
A14
A13
A12
A11
A10
A9
A8
RD*
MEMRQ*
BHE
ALE*
STATUS 0*
BUSRQ*
INTRQ*
NMIRQ*
PBRESET*
INTRQ2* (CNTRL*)
PCI [2]
AUX GND
AUX-V
+5 VDC
GND
VBAT
D3/A19 [1]
D2/A18 [1]
D1/A17 [1]
D0/A16 [1]
A7
A6
A5
A4
A3
A2
A1
A0
WR*
IORQ*
IOEXP
INTRQ1*
STATUS 1*
BUSAK*
INTAK*
WAITRQ*
SYSRESET*
CLOCK*
PCO [2]
AUX GND
AUX+V
P2
P4
P6
P1
P3
P5
P8
P10
P12
P14
P7
P9
P11
P13
P16
P18
P20
P22
P15
P17
P19
P21
P24
P26
P28
P30
P23
P25
P27
P29
P32
P34
P36
P38
P31
P33
P35
P37
P40
P42
P44
P46
P39
P41
P43
P45
P48
P50
P52
P47
P49
P51
P54
P56
P53
P55
PIN (CIRCUIT SIDE)
OUTPUT DRIVE
INPUT LOAD
MNEMONIC
PIN (COMPONENT SIDE)
OUTPUT DRIVE
INPUT LOAD
MNEMONIC
REQ
REQ
1
REQ
REQ
40
3
3
3
3
3
3
3
3
53
53
53
53
53
53
53
53
1
1
1
1
1
1
1
1
55
55
55
55
55
55
55
55
1
1
1
1
1
1
1
1
55
55
55
55
55
55
55
55
1
1
1
1
1
1
1
1
55
55
55
55
55
55
55
55
1
1
1
1
1
1
1
55
55
55
55
1
1
1
1
3
55
52
REQ
REQ
REQ
Notes:
REQ indicates required connection.
[1] High order address bits multiplexed over data bus.
[2] PCI connected to PCO.
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