December 6, 2004 68P81083C20-D
7-12 Controller Section Theory of Operation: MicroprocessorOperation
An option can reset the radio by driving the LH RESET line to a logic 1. This gets buffered by Q0409
and Q0425 and goes to the reset input of SLIC (U0104-A8). This then causes the reset input of the
µP (U0103-50) RESET to go to a logic 0 resulting in the µP restarting operation.
General Purpose Input/Output
(Refer to IO Buffers schematic page 10-46 for reference)
1. Five general purpose I/O lines (GP I/O 2 through GP I/O 6) are provided to interface to exter-
nal options. Each of these lines is configured under software control to be either an input or
an “open collector” output. To make an I/O line an input the corresponding output line is set to
a logic 0; for example to make GP I/O 6 (J0403-7) an input pin, OUT 6 (U0104-K8) is set to a
logic 0. This turns off Q0423 and allows an external device to either turn on or off Q0424
which is sensed by U0104-H2 IN6/RTSB.
2. The GP I/O 2 line is different to the other 4 GP I/O lines. The output transistor (Q0425) can
drive an external relay (HLN4435 or similar) for use with the vehicle horn or lights. This can
also drive a non relay device, but the device must be designed to take a SW B+ input.
3. Selected GP I/O lines have secondary functions. If the line is used for the secondary function
then it can not be used as an I/O line. The following secondary functions are supported (not
all radio models support the RS-232 function, refer to the description for your radio).
The 470 pF and 10 nF capacitors serve to filter out any AC noise which may ride on the GPIO lines.
MicroprocessorOperation
(Refer to schematic page 10-23 for reference)
For this radio, the µP, U0103, is configured to operate in one of two modes, expanded and bootstrap.
In expanded mode the µP uses external memory devices to operate, whereas in bootstrap operation
the µP uses only its internal memory. In normal operation of the radio the µP is operating in
expanded mode as described below. See “Bootstrap Microprocessor Operation” on page 16 for
bootstrap information.
Normal (=Expanded) Microprocessor Operation
In expanded mode on this radio, the µP has access to 3 external memory devices; U0100
(EEPROM), U0101 (SRAM) U0102 (FLASH EEPROM). In addition the µP has access to U0104
(SLIC). Also, within the µP there are 1 Kbytes of internal RAM and 512 bytes of internal EEPROM,
as well as logic to select external memory devices.
Table 7-2. Secondary I/O Functions
I/O line Standard VRM500 Alternate Flashport
GP I/O 2 Horn/Lights Horn/Lights External
Alarm Out
n/a
GP I/O 3 PTT Data PTT n/a Bootstrap Vpp
GP I/O 4 Not Used Not used RS-232
TX Data
Bootstrap Data
GP I/O 5 Car Radio
Mute
Not used RS-232
CTS
n/a
GP I/O 6 Hub-Monitor Not used RS-232
RTS
n/a
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