W65C816S Datasheet, PDF (60/62 Pages) List of Unclassifed Manufacturers – Microprocessor

The Western Design Center, Inc.
W65C816S Data Sheet
8.19 Interrupt Priorities
The following interrupt priorities will be in effect should more than one interrupt occur at the same time:
Highest Priority
Lowest Priority
RESB
ABORTB, NMIB, IRQB
8.20 Transfers from 8-Bit to 16-Bit, or 16-Bit to 8-Bit Registers
All transfers from one register to another will result in a full 16-bit output from the source register. The
destination register size will determine the number of bits actually stored in the destination register and the
values stored in the processor Status Register. The following are always 16-bit transfers, regardless of the
accumulator size: TCS, TSC, TCD and TDC
Note: PHP and PLP are always 8 bit operations.
8.21 Stack Transfers
When in the Emulation mode, a 01 is forced into SH. In this case, the B Accumulator will not be loaded into
SH during a TCS instruction. When in the Native mode, the B Accumulator is transferred to SH. Note that in
both the Emulation and Native modes, the full 16 bits of the Stack Register are transferred to the A, B and C
Accumulators, regardless of the state of the M bit in the Status Register.
8.22 BRK Instruction
The BRK instruction for the NMOS 6502, 65C02 and 65C816 is actually a 2 byte instruction. The NMOS
device simply skips the second byte (i.e. doesn’t care about the second byte) by incrementing the program
counter twice. The 65C02 and 65C816 does the same thing except the assembler is looking for the second byte
as a “signature byte”. With either device (NMOS or CMOS), the second byte is not used. It is important to
realize that if a return from interrupt is used it will return to the location after the second or signature byte.
8.23 Accumulator switching from 8 bit to 16 bit
Care must be taken when switching from 16 bit mode to 8 bit mode then to 16 bit mode. The B register is
restored so that the following code shows a potential problem:
Here BOB = $2301 and NOT $000V
LONGA
REP
LDA
STA
LONGA
SEP
LDA
STA
LONGA
REP
STA
ON
#$20
#$2345
MIKE
PFF
#$20
#$01
SAM
ON
#$20
BOB
The Western Design Center
W65C816S
60