Zilog Z86193 - Manual (Page 62)

Z8
®
CPU
User Manual
UM001604-0108 Input/Output Ports
55
open-drain output, the data returned is the value forced on the output pin by the external
system. This may not be the same as the data in the output register. Reading input bits of
Port 2 also returns data on the external pins. However, inputs under handshake control
return data latched into the input register via the input strobe.
Handshake Operation
Port 2 can be placed under handshake control by programming bit 6 in the Port 3 Mode
Register (see
Figure 42 ). In this configuration, Port 3 lines P31 and P36 are used as the
handshake control lines DAV2 and RDY2 for input handshake, or RDY2 and DAV2 for
output handshake.
Handshake direction is determined by the configuration (input or output) assigned to bit 7
of Port 2. Only those bits with the same configuration as P27 are under handshake control.
Figure 43 displays the bit lines of Port 2 and the associated handshake lines of Port 3.
Figure 42. Port 2 Handshake Configuration
Figure 43. Port 2 Handshaking
D7 D6 D5 D4 D3 D2 D1 D0
(Write-Only)
Port 3 Mode Register
Register F7h
1 P31 = DAV2/RDY2 P36 = RDY2/DAV2
0 P31 = Input (T
IN
) P36 = Output (T
OUT
)
Port 2 Handshaking
Handshake Controls
DAV2 and RDY2
(P31 and P36)
P27
Port 2 (I/O)
P20