Lexicon RV-8 Service Manual page 103

Lexicon
Audio Input Port
Signals: DEC_IN_FSI, DEC_IN_SCKI, DEC_SDI
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This port takes as input I S audio data DEC_SDI synchronous with DEC_IN_SCKI. A frame start pulse is
P
P
also utilized, DEC_IN_FSI. These signals are sourced from the AVRX FPGA. This data is multiplexed into
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the Format Decoder from one of two sources. I S data may come from the Main zone S/PDIF input block
P
P
or from one of six ADCs on the Analog I/O Board.
Chip Clock
Signals: CLK12500C, XTALO, PLLVDD, FILT1. FILT2, CLKSEL, PLLVSS
There are two possible methodologies of providing a global clock signal to the Format Decoder. The
default topology consists of U30, a 12.288MHz 3.3V oscillator. R107 places the output of U30 into the
path of the CLKIN pin. R108 ties the oscillator enable high, causing it to generate the clock.
The second clock source is from the system clock signal CLK12500C. R106 would pass this clock signal
along to the Format Decoder in this option. Naturally, the other two options would have to be disabled and
taken out of the path. This topology has been determined to be not practical due to the differences in
internal topologies between the Format Decoder and the SHARCs. As a result, this option is not
implemented.
FB13 provides a high frequency filtered version of the 2.5VA supply, which in turn is a high frequency
filtered version of the digital 2.5V supply. This double filtered supply voltage drives the internal Phase
Lock Loop of the Format Decoder at the PLLVDD pin. C100 provides local bulk capacitance for this
supply rail through the FILT1 pin.
The internal PLL circuitry requires external band-pass filtering, which is provided via the FILT2 pin by
R99, C98, and C99.
CLKSEL selects the source clock for all internal logic in the Format Decoder, and is controlled by
software. When this signal is low, the internal clock source is the internal PLL. When high, then all internal
logic is driven by the CLKIN pin directly. This signal is significant during the boot phase of RV-8 when the
algorithm FLASH U19 is being loaded. Writing to this FLASH can only happen reliably when CLKSEL is
high.
PLLVSS is connected to digital ground. This is the ground return pin for the internal PLL.
SDRAM Interface
Signals: SD_CS/, SDCKE/, SDCLKI, SDCLKO, DQM0/, DQM1/, SD_CAS/, SD_RAS/, SDWE/
SDRAM is not implemented for the Format Processor. As such, these pins are all pulled high by RP5,
RP6, and RP7.
FLASH Interface
Signals: CRY_NVCS/, CRY_NVWE/, CRY_FLCS/, CRY_NVOE/, DELWE/, NVCS, CRY_A[19:0],
CRY_D[7:0], GPIO20, GPIO21
The format processor utilizes a 512Kx8 FLASH RAM (U19) for algorithm storage. The algorithms are
loaded into the FLASH during the boot phase. Due to a bug in the silicon for the CS49400, the write
enable for the FLASH must be delayed approximately 10nS in relation to the address bus CRY_A[19:0].
This is accomplished by R50/C21 which slows down the falling edge of CRY_NVWE/, effectively delaying
it by approximately 5nS. This signal is OR'ed with the original CRY_NVWE/ to better align the rising edge
of DELWE/ with the address bus so that the hold time will not be violated. An additional 5nS is picked up
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