Static Random Access Memory (Sram) - Motorola MCX600E Service Manual

Open Controller
2.15

Static Random Access Memory (SRAM)

The SRAM (U0103) contains temporary radio calculations or parameters that can change very
frequently, and which are generated and stored by the software during its normal operation. The
information is lost when the radio is turned off. The device allows an unlimited number of write
cycles. SRAM accesses are indicated by the CS signal U103-20 (which comes from U101-CSGP2)
going low. U0103 is commonly referred to as the external RAM as opposed to the internal RAM
which is the 768 bytes of RAM which is part of the 68HC11K1. Both RAM spaces serve the purpose.
However, the internal RAM is used for the calculated values which are accessed most often.
Capacitor C0133 serves to filter out any ac noise which may ride on +5V at U0103.
2.16 Blank Control Head
The blank control head provides the connector to the hand held control mic or head.
2.16.1 Power Supplies
The power supply to the Control Head is taken from the host radio's FLT A+ voltage via connector
J0801(K2) / J0901(K3) pin 2 and the regulated +5V via connector J0801(K2) / J0901(K3) pin 10.
The voltage FLT A+ is at battery level and is used for the LEDs, the back light and to power up the
radio via the On / Off button. The stabilized +5 volt is used for the (display, the display driver,-K3
only) the shiftregister and the keypad buttons.
2.16.2 Power On / Off
The On/Off button when pressed switches the radio's voltage regulators on by pulling ON OFF
CONTROL to high via D0825(K2) / D0925(K3) and connects the base of D0825(K2) / D0925(K3) to
FLT A+. This transistor pulls the line ANALOG 3 to low to inform the µP that the On/Off button is
pressed. If the radio is switched off, the µP will switch it on and vice versa. If the On/Off button is
pressed and held while the radio is on, the software detects a low state on line ANALOG 3 and
switches the radio off.
2.16.3 Electrostatic Transient Protection
Electrostatic transient protection is provided for the sensitive components in the Control Head by
diodes VR0801 - VR0809(K2) / VR0901 - VR0909(K3). The diodes limit any transient voltages to
tolerable levels. The associated capacitors provide Radio Frequency Interference (RFI) protection.
2.16.4 Reversible Control Head
The control head is connected to the RF transceiver by means of a short flexible ribbon cable. This
allows the control head to be mounted either way up in relation to the body of the transceiver. This
means that the transceiver can be mounted in the most cosmetically pleasing and most efficient
cooling orientation and still have the user interface the "right way" up.
4-8 Theory of Operation