Timing Control Unit is for short TCU, which will handle the scheduling of individual events with a quarter bit precision.
The TCU is based on a quarter bit counter (13/12 MHz = 1.083 MHz), which wraps at a programmable value. An interruption is generated when the counter wraps (Frame interrupt). The current value of this counter is available at any time. The wrap value can be set at any time. To assure a predictable behavior this value should only be set by the programmer “far” from the wrap time, to make sure this new value will be taken into account the next time.
The programmer can define events associated to particular counter values (dates). When the counter equals the given date, the action associated to the event will take place.
The events are contained in a table of events split into a programming table and an active table. Only the events in the active table are compared to the counter value. The programming table allows preparing a full sequence of events which will be transferred to the active table when the counter wraps.
A force signal allows transferring events from the programming table to the active table immediately.
The event table has 60 entries, split into 8 areas, TC_AREA_0 to TC_AREA_7, which differ by their force transfer signal condition only. TC_AREA0 can contain up to 25 events, numbered 0 to 24 and TC_AREA_x (where x can be 1 to 7) can contain up to 5 events, numbered 25+5*(x-1) to 25+5(x-1)+4 (for example area 1 contains event number 25 to 29).
● Quarter bit precision.
● 60 entries event table.
● Programmable counter wrap value.
TCU Typical Operation
A typical application would use the TCU to schedule the events needed by the GSM protocol for one frame.
The event associated with the frame 1, are programmed while the frame 0 events are treated. The programmed events will become active when the counter wraps. The maximum number of events that can be programmed for a single frame is limited to 60 (using the eight programming areas).
A manual “Force Active” signal can be sent by the programmer to a given programming area to allow an immediate transfer of the programmed events to the active area. The eight programming areas have separate “Force Active” signals.
When needed, the programmer can change the timer wrap value to compensate for time drift between the mobile device and the base station.
Following is a list of events that can be controlled by the TCU:
-- RF_CTRL pin control
· set RF_CTRLx/clear RF_CTRLx where x is the number of TCO pins.
-- RF interface control
· enable/disable GMSK modulator
· enable/disable power on RF interface transmit IQ DAC
· enable/disable power on RF interface receive IQ ADC
· enable/disable transmit on RF interface (when disabled, TX DAC output is high impedance)
· enable/disable RF interface reception decimator
-- To RF SPI (Pulse)
-- To AFC DAC controller (Pulse)