There are actually 16 attainable four-little bit command codes, and twelve of them are assigned. Aside from the distinctive dual address cycle, the the very least substantial bit on the command code implies no matter if the following details phases absolutely are a browse (details sent from goal to initiator) https://nathanlabsadvisory.com/ensuring-secure-payment-processing-with-pci-dss-compliance-certification-in-the-usa/