Model 2116B Keyboard Interface; Model 340 Telemetry Interface - GE Corometrics 126 Service Manual

Model 2116B Keyboard Interface

Model 340 Telemetry Interface

4-40
Theory of Operation: Communications Board
The keyboard interface consists of a data latch (U7), a status receive buffer (U8), a
control latch (U6), and a PAL device (U15). Data is latched into U7 by an inverted
version of the incoming STB* signal. This signal is inverted in the PAL device.
The STB* signal is buffered through U8 before going to the PAL device for static
protection. Once the STB* signal goes low, the PAL device IBF output goes high
(tells keyboard that the monitor cannot accept any more data). After the STB* line
goes high, the PAL-generated DATAVA* signal (goes to U8 status port) is read by
the processor signaling that data is available. The processor then reads the data by
pulsing the DATARD* line to U7. The PAL device then sets the DATAVA* line
high. The IBF line to the keyboard goes low (signaling to the keyboard that the
monitor can accept more data) when the processor clears the IBF latch. This gives
the processor time to read the data and activate the INVLD* line if the nibble was
bad before the next nibble is sent. Control information is sent to the keyboard via
three lines from latch U6. A KBDRST* line resets the keyboard, a KBDBUSY*
tells the keyboard to put up a busy message (due to recorder being off or busy
printing previous message), and a KBDINVLD* tells the keyboard that the monitor
received an invalid message. The status lines from the keyboard consists of a
KBDIN* line which signals that the keyboard is plugged in, and a KBDMARK* line
which pulses for a one-second minimum to print an event mark. These lines are read
through buffer U8.
The +5 V power for the keyboard is created from VR1 using the +12 V source. This
is done for static protection and for reliability reasons.
The telemetry interface consists of eight digital input status/mode lines and four
analog inputs. The analog lines (TECG, TMECG, TELMAUDIO, TTOCO) are all
passed to the Main Motherboard which in turn feed the DSP Board and Ultrasound
Board. The eight status lines are buffered and read by the main processor.
120 Series Maternal/Fetal Monitor
2015590-001
Revision B