Stanford Research Systems RGA100, Operating Manual And Programming Reference

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10-6 Description of Schematics
SRS Residual Gas Analyzer
Description of Schematics
Schematic name: QMSE_T1
Microprocessor
An MC68HC11E9 microcontroller is used to control the system and to communicate with
the host computer. This central processing unit (CPU) also has RAM, ROM, EEPROM,
UART, octal 8-bit A/D converter, counter timers, and a multiplexed address/data bus to
accommodate an external 32Kx8 RAM. The ROM is used for program storage, the RAM
for data storage, the EEPROM contains calibration values for the particular unit.
The power-up reset and power-fail interrupts are provided to the CPU by U100, a
MAX705.
Digital I/O Ports
The microprocessor’’s I/O ports are assigned as follows:
PA0 -RTS Low indicates that the host computer is ready for RS232 data.
PA1 -BUSY Low indicates that the 16-bit signal A/D converter is busy.
PA2 CAL_EN High enables modification of EEPROM calibration data.
PA3 LE_DAC18 Set high to latch SPI data into 18-bit (RF control) D/A converter.
PA4 -CS_DAC8 Strobe low to assert CS to octal 8-bit DAC.
PA5 LD_LEDS Strobe high to load LED data into output register.
PA6 LD_MPX Strobe high to load multiplexer data into output register.
PA7 LD_MISC Strobe high to load miscellaneous data into output register.
PB
0-7 A8-15 High address bits for external RAM
PC
0-7 A0-7 & D0-7 Multiplexed address and data bits for external RAM
PD0 RXD RS232 data received from host computer.
PD1 TXD RS232 data transmitted to host computer.
PD2 SPI_IN Serial peripheral interface data from 16-bit A/D converter.
PD3 SPI_OUT Serial peripheral interface data to 8 and 18-bit D/A converters.
PD4 SPI_CLK Serial peripheral interface data clock.
PD5 -CTS Low to allow host computer to send RS232 data.
PE0 +24/6 A/D input: +24VDC supply divided by 6.
PE1 RF_CT/5 A/D input: RF primary voltage divided by 5.
PE2 RF_PRI A/D input: RF primary current: 1V/400mA
PE3 GND A/D input: 0 VDC
PE4 GND A/D input: 0 VDC
PE5 FOCUS_I
A/D input: focus plate ion current: 1V/5
P
A
PE6 FIL_DUTY A/D input: filament heater duty cycle: 1V/20%
PE7 FIL_PRI A/D input: filament heater primary current: 3V/A