PK-232 TECHNICAL MANUAL
CHAPTER 3 – THEORY OF OPERATION
PK232TM Rev. A 5/87
3-4
Page 14
3.3.2
Memory
The PK-232 memory consists of 48 kB of EPROM at U2 and U3, and 16 kB of static RAM
at U4 and U5.
U2 is a 27256 EPROM which occupies the 32 kB address space between $0000 and
$7FFF.
EPROM U3 is a 27128 occupying 16 kB from $8000 to $BFFF.
The read-write memory consists of two 6264 8 kB volatile static RAMs, U4 occupying
$C000-DFFF and U5 at $E000-FFFF. Both U4 and U5 have their power backed up by bat-
teries when the system power is off.
The 74LS139 address decoder at U10 receives address bits A13, A14 and A15 from the
CPU, and provides chip enables for U3, U4 and U5. Address bit A15 is used directly as the
chip enable for the U2 EPROM at address $0000.
U17 pin 8 provides a Memory Read (OE*) line for U2, U3, U4 and U5. U17 pin 11 is the
Memory Write (·WE*) line for the RAMs U4 and U5.
3.3.3
8536 CIO Counter/Timer and Parallel I/O Unit
U6 is an 8536 CIO chip which provides 20 parallel I/O pins and three timers. This chip re-
ceives address bits A0, A1 and A6 from the CPU. The PK-232's firmware addresses the
8536 by forcing all other address bits high, yielding these addresses:
$BC - Parallel port A data
$BD - Parallel port B data
$BE - Parallel port C data
$BF - Control port
The 8536 uses the CPU's 4.0 MHz clock on the PCLK input (pin 16). The 8536 interrupt
has priority over the interrupt from the 8530 (U7).
Parallel port A controls several different functions in the PK-232:
Bit
U6 Pin
Function
Sense
Direction
––––––––––––––––––––––––––––––––––––––––––––––––––––––
PA7
26
Squelch
In
PA6
27
RTTY transmit data
Out
PA5
28
Wide shift enable
Pos
Out
PA4
29
Tone enable
Pos
Out
PA3
30
Calibration
In
PA2
31
FSK enable
Pos
Out
PA1
32
CW key closed
Neg
Out
PA0
33
Narrow shift enable
Neg
Out
PA3 counts the transition on the digital output of U40, the 2206 tone generator.
PA2 when high enables FSK for Packet and RTTY; when low PA2 enables CW. PA5, PA2
and PA0 work together to determine the shift the PK-232 uses:
Summary of Contents for PAKRATT PK-232
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