dp8344b National Semiconductor Corporation, dp8344b Datasheet - Page 13

• Manufacturer Part Number: dp8344b
• Description: Biphase Communications Processor?bcp
• Manufacturer: National Semiconductor Corporation

2 0 CPU Description
The CPU is a general purpose 8-bit microprocessor capa-
ble of 20 MHz operation It contains a large register set for
standard CPU operations and control of the transceiver
The reduced instruction set is optimized for the communica-
tions environment The following sections are an architec-
tural and functional description of the DP8344B CPU
2 1 CPU ARCHITECTURAL DESCRIPTION
2 1 1 Register Set
This section describes the BCP’s internal CPU registers It is
a general overview of the register structure and the func-
tions mapped into the CPU register space It is not a de-
tailed or exhaustive description of every bit For such a de-
scription please refer to Section 6 2 Register Set Refer-
ence Also the Remote Interface Configuration register
by the remote system) and is described in Section 6 3 Re-
mote Interface Reference
The register set of the BCP provides for a compliment of
both special function and general purpose registers The
special function registers provide access to on-chip periph-
erals (transceiver timer interrupt control etc ) while the
general purpose registers maximize CPU throughput by min-
imizing accesses to external data memory The CPU can
address a total of 44 8-bit registers providing access to
The CPU addresses internal registers with a 5-bit field ad-
dressing 32 locations generically named R0 through R31
The first twelve locations (R0 – R11) are further organized by
function as two groups of banked registers (A and B) as
shown in Figure 2-1 Each group contains both a main and
an alternate bank Only one bank is active for group A and
one for bank B and thus accessible during program execu-
tion Switching between the banks is performed by the ex-
change instruction EXX which selects whether Main A or
Alternate A occupies R0 – R3 and whether Main B or Alter-
nate B occupies R4 – R11








RIC
20 general purpose registers
8 configuration and control registers
4 transceiver access registers
2 8-bit accumulators
4 16-bit pointers
16-bit timer
16 byte data stack
address and data stack pointers
is not accessible to the BCP (being accessible only
13
FIGURE 2-1 Register Map
TL F 9336 – 32