I have one or two communication questions.

sanhuasr

I have one or two communication questions. [Copy link]

1. Can I read the values of multiple discontinuous addresses during a modbus read operation? 2. The communication speed is 1Mbps, the carrier cycle is 8K, and 7 words can be sent per carrier cycle. The chip uses SSI (serial synchronous interface) for communication. Is there a related module that supports conversion to USB?

chunyang

ModBus is a one-master-multiple-slave network protocol. Each terminal corresponds to an address. Of course, it can only communicate with one terminal node at a time. Only the broadcast mode is one-to-many for the entire network, but that is not "reading". As for the USB support issue, it depends on your serial port hardware. If it meets the standard serial port (RS232), it will have it, otherwise it will not.

huo_hu

No, non-continuous addresses can only be read multiple times. The 03 function has only one starting address, so it is impossible to support non-continuous addresses. I don't know that

sanhuasr

chunyang posted on 2017-12-14 11:13 ModBus is a one-master-multiple-slave network protocol. Each terminal corresponds to an address. Of course, it can only communicate with one terminal node at a time. Only the broadcast mode is one-to-many...

I didn't explain clearly, in the case of one master and one slave, will ModBus support register access with random addresses? For example, the normal communication format: header code + slave address code + register start address + register number + checksum is now changed to: header code + slave address code + register start address 1++register start address 4+register start address 7+register number + checksum. Is it supported?

sanhuasr

huo_hu posted on 2017-12-14 11:28 No, non-continuous addresses can only be read multiple times. The 03 function has only one starting address, so it is impossible to support non-continuous addresses. I don't know...

03 supports continuous operation, but I don't know if it supports arbitrary multiple address read operations? If I define the communication protocol myself, can it meet the above requirements?

huo_hu

sanhuasr posted on 2017-12-14 19:42 I didn't make it clear, in the case of one master and one slave, will modbus support register access with random addresses? For example, the normal communication format is: header code + slave...

Clearly no, the 03 read instruction has a fixed format, which is a national standard, you can look it up.

huo_hu

sanhuasr posted on 2017-12-14 19:43 03 supports continuous operation, but I don't know if it supports arbitrary multiple address read operations? If you define the communication protocol yourself, can it meet the above requirements?

You can do this yourself, but it cannot be called modbus

chunyang

sanhuasr posted on 2017-12-14 19:42 I didn't make it clear, in the case of one master and one slave, will modbus support register access with random addresses? For example, the normal communication format is: header code + slave...

If you use Modbus, you can only follow the ModBus specification. No matter you have one master and several slaves, you should treat it as one master and multiple slaves. If your system is just one master and one slave and they are all designed by yourself, and do not need to be compatible with other ModBus devices, then there is no need to use ModBus.