W65C816S Datasheet, PDF (19/62 Pages) List of Unclassifed Manufacturers – Microprocessor

The Western Design Center, Inc.
3.13 Reset (RESB)
W65C816S Data Sheet
The Reset (RESB) active low input is used to initialize the microprocessor and start program execution. The Reset input
buffer has hysteresis such that a simple R-C timing circuit may be used with the internal pull-up device. The RESB signal
must be held low for at least two clock cycles after VDD reaches operating voltage. Ready (RDY) has no effect while RESB
is being held low. The stack pointer must be initialized by the user's software. During the Reset conditioning period the
following processor initialization takes place:
D=0000
DBR=00
PBR=00
Registers
SH=01, SL=*
XH=00, XL=*
YH=00, YL=*
A=*
Signals
E=1
VDA=0
MX=1 VPB=1
RWB=1 VPA=0
P Register
N
V
M
X
D
I
*
*
1
1
0
1
Z C/E
*
*/1 *=not initialized
When Reset is brought high, an interrupt sequence is initiated
• STP and WAI instructions are cleared
• RWB remains in the high state during the stack address cycles.
• The Reset vector address is 00FFFC,D.(see Table 6-1 for Vectors)
• PC is loaded with the contents of 00FFFC,D
3.14 Valid Data Address (VDA) and Valid Program Address (VPA)
The Valid Data Address (VDA) and Valid Program Address (VDA) output signals indicate valid memory
addresses when high and are used for memory or I/O address qualification.
VDA VPA
0
0
0
1
1
0
1
1
Internal Operation Address and Data Bus available. The Address Bus may be invalid.
Valid program address-may be used for program cache control.
Valid data address-may be used for data cache control.
OpCode fetch-may be used for program cache control and single step control
3.15 VDD and VSS
VDD is the positive supply voltage and VSS is system logic ground.
3.16 Vector Pull (VPB)
The Vector Pull (VPB) active low output indicates that a vector location is being addressed during an interrupt
sequence. VPB is low during the last two interrupt sequence cycles, during which time the processor loads the PC
with the interrupt handler vector location. The VPB signal may be used to select and prioritize interrupts from
several sources by modifying the vector addresses.
The Western Design Center
W65C816S
19