GP2021
12 CHANNEL CORRELATOR
Fig. 4 shows a block diagram of the correlator. It consists
of the following blocks:
Clock Generator
The Clock Generator block divides the frequency of the
master clock CLK_T/CLK_I by 6 or 7 to give the internal multi–
phase set of clocks. When in Real_Input mode CLK_T/CLK_I
will normally be a 40MHz clock, which is divided by 7. When
in Complex_Input mode it will normally be at 35MHz which is
divided by 6. The SAMPCLK pin is an output giving a 4:3
mark–to–space ratio clock at 40 MHz / 7 (= 5·714MHz) in
Real_Input Mode.
The Clock Generator also produces the MICRO_CLK
signal at half the master clock frequency (20 MHz for
Real_Input mode, 17.5 MHz for Complex_Input mode) with a
1:1 mark–to–space ratio. This signal is output on the
MICRO_CLK pin in Standard Interface mode. However, its
main purpose is that of a synchronising clock to the memory
control logic in ARM System Mode and it is from this that the
processor clock output, MCLK, is derived.
CLK_T
CLK_I
SAMPCLK
MICRO_CLK
MEAS_INT
ACCUM_INT
MULTI–
PHASE
CLOCK
GENERATOR CLOCKS
TRACKING
MODULE
CHANNEL 0
REGISTER
SELECTS
ADDRESS
DECODER
A<9:2>
TIMEBASE
GENERATOR
TIC
TRACKING
MODULE
CHANNEL 1
32 BIT BUS
TRACKING
MODULE
CHANNEL 2
BUS
INTERFACE
D<15:0>
CONTROL
INTERNAL
SAMPCLK
SIGN0 &
MAG0
SIGN1 &
MAG1
V
DD
V
SS
LATCHED
SIGN0 & MAG0
SAMPLE
LATCH
LATCHED
SIGN1 & MAG1
POWER SUPPLY
STATUS
REGISTERS
TRACKING
MODULE
CHANNEL 3
SYSTEM STATUS
BITS
TRACKING
MODULE
CHANNEL 11
Fig. 4 Correlator block diagram
Timebase Generator
The Timebase Generator produces 4 important timing
signals: ACCUM_INT, TIC, MEAS_INT and TIMEMARK.
ACCUM_INT is an interrupt provided to control data transfer
between the correlator accumulators and the microprocessor.
It may be detected by means of the ACCUM_INT output or by
reading the ACCUM_STATUS_A register (where bit 15 is a
flag indicating that ACCUM_INT has occurred since the
previous read of this register). ACCUM_INT is cleared by
reading ACCUM_STATUS_A.
After power–up this interrupt occurs every 505.05µs. Its
period can subsequently be changed in one of 3 ways:
1) toggling the FRONT_END_MODE bit of the
SYSTEM_SETUP register,
2) toggling the INTERRUPT_PERIOD bit of the
SYSTEM_SETUP register, or
3) writing directly to the PROG_ACCUM_INT register.
See section ‘‘Detailed Description of Registers” on page 25 for
more information.
TIC is an internal signal with a default period of
99999.90µs. It is used to latch measurement data (Epoch
count, Code phase, Code DCO phase, Carrier DCO phase
and Carrier cycle count) of all 12 channels at the same instant.
Its period can subsequently be changed, by writing to the
PROG_TIC_HIGH and PROG_TIC_LOW registers, or
toggling the FRONT_END_MODE bit of the
SYSTEM_SETUP register.
MEAS_INT is a signal derived from the TIC counter. It may
be used by the microprocessor as a software module
switching interrupt either by using the MEAS_INT output or by
reading the ACCUM_STATUS_B or MEAS_STATUS_A
register. MEAS_INT is activated at each TIC and 50 ms before
each TIC so long as the TIC period is greater than 50 ms. If the
TIC period is less than 50 ms, MEAS_INT is activated only at
each TIC. It is cleared by reading either the
ACCUM_STATUS_B or MEAS_STATUS_A register,
depending upon the MEAS_INT_SOURCE bit of the
SYSTEM_SETUP register.
TIMEMARK is also derived from TIC and may be output on
one of the discrete output pins. This signal is intended to be
used as an accurate 1 Pulse Per Second timing reference,
aligned to UTC (Universal Time Co–ordinated system), with a
pulse width of 1ms.
TIMEMARK has two methods of operation but in both
8
MITEL [ MITEL NETWORKS CORPORATION ]
