Radio Shack 16B Technical Reference Manual

6809E CPU
The
6809E is one
of the most
powerful 8-bit
microprocessors
available.
The
architectural
features include two
16-bit index
registers, two 16-bit
stack
pointers, and two
8-bit accumu-
lators. A block
diagram
of
the
6809E
CPU
is
shown in Figure
2.
Figure 3 shows
the
programming
model of the
6809E CPU. A
and B are
the two 8-bit
accumulators.
They are used
for
arithmetic
operations and
data
manipulation. Also A and B
may be
combined to
form the 16-bit
register
D,
with A as the
most significant byte.
The
Program Counter
(PC) is
used
primarily for the
CPU
to
keep
track of its location in
memory.
X
and
Y
are both
16-bit index
registers. They are used by
software
to
point to
certain data or
program segments in
memory. The
Hardware Stack
Pointer (S) is used
by the
processor
during subroutine
calls and interrupts. Also
available
in the
6809E
is
the User Stack (U)
which has
all of
the
flexibility of the
Hardware Stack, and is
controlled
exclusively
by
the
programmer. In
addition
to all
of
the
pointers and
registers the
6809E
also has a
Direct Page
Register (DP) and a
Condition Code Register
(CC). The
Direct Page
Register
contents are used as
the upper 8
bits of address
when the
direct
addressing mode is used.
This allows the
direct mode to
be used
any place in
memory. The
Condition Code
contains all
of
the
arithmetic flags plus
the mask
bits for IRQ*
and
FIRQ*. These arithmetic
flags are used to
control all
of the
conditional branches. The mask
bits allow the
CPU to ignore
all but the
non-maskable
Interrupt.
TSC
PC
DP
D0-
D7
ffl
CC
ALU
vcc
Vss
IR
f f \
RESET"
NMI*
Interrupt
Control
FIRQ"
IRQ"
*
BUSY
Timing
FIGURE 2.
6809E
CPU BLOCK
DIAGRAM
16

Radio Shack 16B Specifications

General

Brand	Radio Shack
Model	16B
Category	Desktop
Language	English