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Rev 1.0
33
Communication Interfaces
5
Communication Interfaces
The SC5507A has a PXI express interface, while the SC5508A has 2 communication interfaces:
1.
USB and SPI
2.
USB and RS232
This section will examine the communication aspects of the product, focusing on data transfer to and
from the device on each interface. Although the registers are identical for all interfaces, there are subtle
differences in the implementation of the interfaces to transfer the data.
Communication Data Format
All data sent and received by all interfaces is sent as buffers of unsigned bytes. For example, to change RF
frequency of the device to 3 GHz we perform the following:
1.
Frequency is sent in 1000
th
of Hertz, so the data that represents the frequency is
3,000,000,000,000 milli-Hertz.
2.
This number can be represented by a 64-bit unsigned long, and in Hexadecimal is 0x 0000 0574
FBDE 6000. The least 7 bytes are necessary to represent all frequencies allowable for this device,
so the MSB is used to hold the register address.
3.
A buffer needs to be 8 bytes for register RF_FREQUENCY (address 0x10), so the byte array buffer
to be sent would be:
[0x10][0x00][0x05][0x74][0xFB][0xDE][0x60][0x00]
The register address byte [0x10] is the first member (MSB) of the buffer to be sent.
USB Interface
There are 2 transfer types for the USB interface.
•
Control transfer
•
Bulk transfer
Control Transfer
The USB control transfer parameters are:
ENDPOINT_IN
0x80
ENDPOINT_OUT
0x00
TYPE_VENDOR
0x40
RECIP_INTERFACE
0x01
Bulk Transfer
The USB bulk transfer parameters are:
ENDPOINT_IN
0x81
ENDPOINT_OUT
0x02