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HI-3111PCMF 参数 Datasheet PDF下载

HI-3111PCMF图片预览
型号: HI-3111PCMF
PDF下载: 下载PDF文件 查看货源
内容描述: 航空电子与CAN收发器集成控制器 [Avionics CAN Controller with Integrated Transceiver]
分类和应用: 电子控制器航空
文件页数/大小: 53 页 / 178 K
品牌: HOLTIC [ HOLT INTEGRATED CIRCUITS ]
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HI-3110  
The CAN standard divides the bit time into four segments,  
BIT TIMING  
namely, synchronization segment (Sync Seg), propagation  
time segment (Prop Seg), phase buffer segment 1 (Phase  
Seg1) and phase buffer segment 2 (Phase Seg2). This is  
illustrated in figure 8. The HI-3110 fixes the Sync Seg at  
1Tq. Prop Seg and Phase Seg1 are treated as one time  
segment, TSeg1, which is programmable from 2Tq to 16Tq.  
Phase Seg2 is a second time segment, TSeg2, which is  
programmable from 2Tq to 8Tq (Note: Not all combinations  
are valid, see below for examples).  
The CAN protocol supports a broad range of bit rates, from a  
few kHz up to 1MHz (Note: the minimum bit rate of the HI-  
3110 is limited to 40kHz by the permanent dominant timeout  
protection of the transceiver). Every node on the network  
has it’s own clock generator (typically a quartz oscillator),  
however the bit rate must obviously be the same for every  
node on the bus. Therefore, each CAN node must be  
configurable to generate the nominal bit rate as a function of  
it’s own oscillator frequency, fOSC. This is done by generating  
a time quanta (TQ) clock, whose period tTQ is related to the  
oscillator frequency by a Baud Rate Prescaler value, BRP as  
follows:  
Synchronization Segment (Sync Seg)  
The Sync Seg is the first segment of the bit time and is used  
to synchronize the various nodes on the bus. A bit edge is  
expected to occur within the Sync Seg.  
tTQ = 2•BRP/fOSC  
(1)  
The TQ clock is used to construct the bit time in terms of time  
quanta, such that one time quantum, Tq, equals one TQ  
clock period, tTQ, as shown in figure 8 below.  
Propagation Time Segment (Prog Seg)  
The Prog Seg is used to compensate for physical delays on  
the bus, which include signal propagation delay time on the  
bus and internal node delay times. For two nodes A and B  
communicating on the bus, Prog Seg must be greater than  
or equal to the sum of both nodes internal delays plus twice  
the bus line propagation delay between the two nodes.  
The CAN system nominal bit rate (BR) is defined in terms of  
the nominal bit time, tb, as  
BR = 1/tb  
(2)  
Therefore, the nominal bit rate is related to the TQ clock  
period by the following relationship  
BR = 1/(tTQ x (number of time quanta per bit))  
(3)  
tOSC  
OSC  
Baud Rate Prescaler  
tTQ  
TQ  
Clock  
Nominal bit time, tb  
Tq  
Sync  
Seg  
Sync  
Seg  
TSeg1 =  
Prop Seg + Phase Seg 1  
TSeg2 =  
Phase Seg2  
TSeg1  
TSeg2  
Sample  
Point  
Figure 8. CAN Bit Time  
HOLT INTEGRATED CIRCUITS  
14  
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