Z89135 Datasheet, PDF (23/66 Pages) Zilog, Inc. – Low-Cost DTAD Controller

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