Agilent Technologies 8453 Operator's Manual page 142

Theory of Operation
Spectrophotometer Processor Main (SPM) Board
7 variance calculation.
Communication between the spectra and signal processor (SSP) and the PDA
front end processor (PFP) on the SDA board is established by a serial
communication link. Processed data and synchronization signals for the PFP
clock frequency are exchanged through the serial bus.
SIMM Memory Module
The SIMM memory module controlled by the dedicated ASIC is used to
expand the memory to 2 MB (add 1 MB module, part number 1818-4271) or
2 × 4 MB (part number 1818-5784) to accomodate more spectra.
Firmware
For an outline of the firmware, see "Firmware Description" on page 43.
36