ZiLOG Z8 Technical Manual

R245 PREO
Prescaler 0 Register
(% F5; Write Only)
10101111111 111
L
COUNT MODE
o = To SINGLE-PASS
1 = To MODULO-N
1...- ______ PRESCALER MODULO
0=64
Figure 12-5. Prescaler 0 Register
and Bit Rate Generation
R241 TMR
Timer Mode Register
(% F1; Read/Write)
~
0 = NO FUNCTION
1 = LOAD To
o = DISABLE To COUNT
1
= ENABLE To COUNT
Figure 12-6. Timer Hode Register
and Bit Rate Generation
(R)
RCVR
DATA
START BIT
I
TRANSITION
~ DETECTED
SHIFT ___ ..
CLOCK
Serial I/O
12.3 RECEIVER OPERATION
The receiver consists of a receiver buffer (SID
[%FO]), a serial-in, parallel-out Shift register,
parity checking, and data synchronizing logic.
The receiver block diagram is shown an part of
Figure 12-1.
12.3.1 Receiver Shift Register
A fter a hardware reset or after a character has
been
received, the Receiver Shift register is
initialized to all 1s and the shift clock is
stopped. Serial data, input through Port 3 pin
P30, is synchronized to the internal clock by two
D-type flip flops before being input to the Shift
register and the start bit detection circuitry.
The ntart bit detection circuitry monitors the
incoming data stream, looking for a start bit (a
High-to-Low input transition). It/hen a ntart bit
is detected, the shift clock logic is enabled.
The TO input is divided by 16 and, when the count
equals 8, the divider outputs a shift clock. This
clock shifts the start bit into the Receiver Shift
register at the center of the bit time. Before
the shift actually occurs, the input is rechecked
to ensure that the start bit is valid. I f the
detected start bit is false, the receiver is reset
and the procesn of looking for a start bit is
repeated. If the start bit is valid, the data is
shifted into the Shift register every sixteen
counts until a full character is assembled (Figure
12-7) •
~ 8 TO COUNTS LATER SHIFTING STARTS
RCVR ______________________________________________________ ~
f
IRQ3
Figure 12-7. Receiver Timing
SHIFT REGISTER CONTENTS
TRANSFERRED
TO RECEIVER
BUFFER
AND IR03 IS
GENERATED
3047-070,3047-026,3047-071 12-3

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English