ISO1050接口问题

ISO1050 这款芯片是不是通讯速率50kbps行不行？能不能支持100个节点？官方datasheet只提到支持ISO11898，而iso11898的速率只有125kbps——1Mbps ，支持的节点数30个

Kailyn Chen：

ISO1050能够支持的速率最大为1Mbps，ISO11898标准是可挂接的节点数最大为30个。但datasheet中有这样一句描述：

 

The ISO11898 Standard specifies a maximum bus length of 40 m and maximum stub length of 0.3 m with amaximum of 30 nodes. However, with careful design, users can have longer cables, longer stub lengths, andmany more nodes to a bus. A high number of nodes requires a transceiver with high input impedance such asthe ISO1050.

但100个节点远大于标准，应该是不可以的。

qin liao1：

回复 Kailyn Chen:

看了下最新数据手册 A CAN network design is a series of tradeoffs, but these devices operate over wide –12-V to 12-V commonmode range. In ISO11898-2 the driver differential output is specified with a 60-Ω load (the two 120-Ω termination resistors in parallel) and the differential output must be greater than 1.5 V. The ISO1050 is specified to meet the 1.5-V requirement with a 60-Ω load, and additionally specified with a differential output of 1.4 V with a 45-Ω load. The differential input resistance of the ISO1050 is a minimum of 30 kΩ. If 167 ISO1050 transceivers are in parallel on a bus, this is equivalent to a 180-Ω differential load. That transceiver load of 180 Ω in parallel with the 60 Ω gives a total 45 Ω. Therefore, the ISO1050 theoretically supports over 167 transceivers on a single bus segment with margin to the 1.2-V minimum differential input at each node. However for CAN network design margin must be given for signal loss across the system and cabling, parasitic loadings, network imbalances, ground offsets and signal integrity thus a practical maximum number of nodes is typically much lower. Bus length may also be extended beyond the original ISO11898 standard of 40 m by careful system design and data rate tradeoffs. For example, CAN open network design guidelines allow the network to be up to 1km with changes in the termination resistance, cabling, less than 64 nodes and significantly lowered data rate.  似乎能支持167个节点，但是受线材、速率等影响远远不到，具体有多少节点没有明确给出。另外我关心能不能支持更低速率，在资料上哪里体现？是看环路延迟tloop？ 如何计算

Kailyn Chen：

回复 qin liao1:

tTXD_DTO限制了ISO1050的最小data rate，为37Kbps。在你的应用中，125Kbps使用ISO1050 没问题。在datasheet 6.9表格的下面有注释：

The TXD dominant time out (tTXD_DTO) disables the driver of the transceiver once the TXD has been dominant longer than (tTXD_DTO)which releases the bus lines to recessive preventing a local failure from locking the bus dominant. The driver may only transmitdominant again after TXD has been returned HIGH (recessive). While this protects the bus from local faults locking the bus dominant itlimits the minimum data rate possible. The CAN protocol allows a maximum of eleven successive dominant bits (on TXD) for the worstcase where five successive dominant bits are followed immediately by an error frame. This along with the (tTXD_DTO) minimum limits theminimum bit rate. The minimum bit rate may be calculated by: Minimum Bit Rate = 11/ (tTXD_DTO) = 11 bits / 300 μs = 37 kbps.

Kailyn Chen：

回复 Kailyn Chen:

不好意思，你的应用是50Kbps，没问题。

qin liao1：

回复 Kailyn Chen:

谢谢