Programming instructions

Downloading and Using Files
User File Data Downloads
Chapter 4 171
NOTE The data in PRAM is static. Firmware writes to PRAM once for the
configuration selected and the hardware reads this data repeatedly. Firmware
overwrites the volatile PRAM memory to reflect the desired configuration only
when the data source or mode (digital communications format) is changed.
Take for example, transmitting a 228-bit user file for timeslot #1 (TS1) in a normal GSM
transmission. Per the standard, a GSM normal channel is 156.25-bits long, with two 57-bit
data fields (114 bits total per timeslot), and 42 bits for control or signalling purposes.
NOTE Compliant with the GSM standard, which specifies 156.25-bit timeslots, the
signal generator uses 156-bit timeslots and adds an extra guard bit every
fourth timeslot.
The seven remaining timeslots in the GSM frame are off. The user file will completely fill
timeslot #1 in two consecutive frames, and will then repeat. See Figure 4-2.
Figure 4-2 Mapping User File Data to a Single Timeslot