参数资料
型号: 74ETL16245
厂商: National Semiconductor Corporation
英文描述: 16-Bit Data Transceiver with Incident Wave Switching
中文描述: 16位数据收发器事件波开关
文件页数: 3/10页
文件大小: 190K
代理商: 74ETL16245
Incident Wave Switching
(Continued)
To demonstrate the incident wave switching capability, con-
sider a VME application. A VME bus must be terminated to
a
2.94V with 190
X
at each end of its 21 card backplane.
The surge impedance presented by a fully loaded VME
backplane is approximately 25
X
. If the output voltage/cur-
rent of an ABTC driver is plotted with this load, the inter-
section at 1.2V for a falling edge and at 1.6V for a rising
edge does not reach the worst case input threshold of a
second ABTC circuit. This is shown in the two figures below.
However, an ETL driver located at one end of the backplane
is able to provide incident wave switching because it has a
higher drive and a tighter input threshold.
Estimated ETL/ABTC Initial Falling Edge Step
TL/F/11654–7
Because ETL has a much more precise input threshold re-
gion, an ETL receiver will interpret its predicted falling input
of 0.85V as a logic ZERO and the initial rising edge of 1.9V
as a logic ONE. This comparison is for the case of a 25
X
surge impedance backplane driven from one end.
Estimated ETL/ABTC Initial Rising Edge Step
TL/F/11654–8
The resulting ABTC and ETL waveform predictions and their input thresholds are compared below. This shows how ETL can
achieve backplane speeds not always possible with conventional TTL compatible logic families.
Comparing the Incident Wave Switching of ETL with ABTC
TL/F/11654–9
3
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