z89136 ZiLOG Semiconductor, z89136 Datasheet - Page 23

• Manufacturer Part Number: z89136
• Description: Low-cost Dtad Controller
• Manufacturer: ZiLOG Semiconductor

Zilog
Port 2. (P27-P20). Port 2 is an 8-bit, bidirectional, CMOS-
compatible I/O port. These eight I/O lines are configured
under software control as an input or output, independent-
ly. Port 2 is always available for I/O operation. The input
buffers are Schmitt triggered. Bits programmed as outputs
may be globally programmed as either push-pull or open-
drain.
Port 2 may be placed under handshake control. In this con-
figuration, Port 3 lines P31 and P36 are used as the hand-
shake controls lines /DAV2 and RDY2. The handshake
DS97TAD0300
Open Drain
OEN
Out
In
1.5
Z89135/136
MCU
Figure 12. Port 2 Configuration
2.3V Hysteresis
P R E L I M I N A R Y
R = 500 K
signal assignment for Port 3 lines P31 and P36 is dictated
by the direction (input or output) assigned to bit 7, Port 2
(Figure 12).
The Auto Latch on Port 2 puts valid CMOS levels on all
CMOS inputs which are not externally driven. Whether this
level is 0 or 1, cannot be determined. A valid CMOS level,
rather than a floating node, reduces excessive supply cur-
rent flow in the input buffer.
Handshake Controls
/DAV2 and RDY2
(P31 and P36)
Port 2
(I/O)
Low-Cost DTAD Controller
Auto Latch
Z89135/136 (ROMless)
PAD
1-23
1