Control Board
4-8 Force FX Electrosurgical Generator C Service Manual
Shared RAM
The 4K x 8 external shared static RAM is provided by an IDT 713425A device (U4) with
semaphore flags. The shared RAM allows the main microcontroller (U5) and the feedback
microcontroller (U11) to share common variables. It functions as a communications
interface between the main and feedback microcontrollers. It also provides additional
general purpose RAM to these microcontrollers.
I/0 Expansion
Three devices provide I/O expansion capabilities:
•One ST microelectronics PSD835G2 programmable systems device
•One ST microelectronics PSD835G2 programmable systems device
•One 82C55 expansion port (U2).
The ST Microelectronics PSD835G2 incorporates 52 individually programmable I/O pins
divided into 6 ports of 8-bits each and 1 port of 4-bits. Of the general I/O pins, 24 can be
alternatively utilized for 24 PLD outputs.
The PSD835G2 also contains 512K x 8 main flash memory, 32K x 8 boot flash memory,
2K x 8 of SRAM, and a power management unit for battery backup. The power
management unit for battery backup is not used by the feedback microcontroller. The I/O
expansion capabilities of the feedback PSD835G2 has a built-in IEEE 1149.1 compliant
JTAG serial port to allow full-chip in-system programmability (ISP).
The main PSD835G2 is #1 on the JTAG chain and the feedback PSD835G2 with the
exception that the 512K x 8 flash memory for the main PSD835G2 is accessed in a bank
switching methodology and the I/O expansion capabilities are configured as outputs for
lamp control, keyboard scanning, and chip selects.
The 82C55 is configured as all inputs, and is used to read the keyboard, keying signals,
accessory switches, and system status flags.
Keyboard Interface and Activation Inputs
The keyboard interface is a simple row and column matrix between three bank select
output lines (BANK0–BANK2) on port A of the PSD835G2 (U3) used by the main
microcontroller and eight keyboard (KBD_D0–KBD_D7) input lines on port A of the
expansion port 82C55 (U2).
Port B of the expansion port 82C55 reads activation inputs from the IsoBloc decoding
circuits on the Power Supply/RF board.
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