RF Technology Eclipse Series Operation And Maintenance Manual page 17

5 CIRCUIT DESCRIPTION
LOOP_DET is a CPU pin that is asserted low if there is dc loop current detected
through the centre tap input of Line2. (See 5.3)
FILTER_OFF is a CPU output that is used to by-pass, when low, the low pass filter in
the Tone Input Circuitry. (See 5.5)
PTT-in is an input from the rear DB25 connector that causes the INT pin of the CPU to
be asserted (low) when 1mA of current is drawn via that pin. If PTT-in is pulled to
ground, through a resistance of at most 3.9kohms, it will cause INT to be asserted. If it
is pulled low via a 2K2 resistor, and as many as three diodes in series, it will still cause
the INT pin to be asserted. This latter example shows that quite complex diode logic
can be used on this pin.
BKGD is a bi-directional I/O pin used to communicate with the core of the CPU. It is
connected to the debug port and is utilised by specialised hardware to control the CPU
externally, even without any firmware being present in the Flash.
DEV_H_L is a CPU output that can be used to generate a test signal in the audio path.
It is currently not used. (See 5.4)
The RESET pin is both a low active input and a low active output to the CPU. If
generated externally to the CPU, it forces the CPU into reset, and if the CPU executes a
RESET instruction this pin will be driven low by the CPU.
Whenever there is insufficient volts (< 4.65V) on pin 2 of the MC33064D (U203), it
will keep its RES output low. After the voltage has met the right level it will assert its
output low for another 200 milliseconds. Thus the CPU will be held in reset until VCC
is at the correct level. Thus the PWR_OK LED will only light when VCC is within
specification, and RESET has been released.
S200 is a momentary push-button switch that, when pressed, will cause the CPU to be
reset.
MOD_PLL_SEL is a serial bus select pin. It is used to select the Modulation PLL chip
(U602). (See 5.6)
LCD_RS, LCD_R/W, and LCD_E are reserved for interfacing to an LCD display
module. Note that this feature has not been implemented.
U205 is used to select whether the Flash or RAM is to be read or written.
U207 is a single supply, 5V, TSOP40 Flash chip of size 8, 16, or 32 Megabits, and is
used to store the firmware.
U208 is a 1, or 4, Megabit Static RAM in an SOP-32 package, and is used for both code
and data. The code in the RAM is copied from the Flash, at start-up.
RF Technology T50 Page 17