16-Bit Isa Bus Interface; Pal Equations - Epson S1D13503 Series Technical Manual

EPSON

1.2 16-Bit ISA Bus Interface

For the purpose of the example shown below, the following conditions apply:
1. Indexed I/O with addresses 0310h and 0311h (see Configuration Options)
2. 128K bytes of display memory occupying $C and $D segments (see Configuration Options)
Note: This memory configuration will conflict with a VGA card installed on the same bus, therefore either a
serial terminal or monochrome display adapter is recommended as the primary console.
This section provides the necessary logic equations and settings to complete the interface between
the S1D13503 and the 16-bit ISA Bus.
Note: A PAL was used instead of discrete logic to reduce external component count.
16-Bit ISA Bus
AEN
REFRESH
SA0–19
SBHE#
SD0–15
SMEMW#
SMEMR#
IOW#
IOR#
IOCHRDY
IOCS16#
LA17–23
MEMCS16#

PAL Equations

The PAL is programmed with the following equations:
A '!' placed before a signal name indicates a logic '0' state.
A '&' indicates a logic 'AND' function.
1. As stated above, the default I/O address is from 0310h to 0311h. The S1D13503 provides inter-
nal decoding of address bits A0 to A9, therefore minimal external circuitry is necessary to pro-
vide signals IOCS# and IOCS16#.
IOCS# is required by the S1D13503 to indicate a valid I/O cycle. In an ISA bus environment,
valid I/O decoding must include addresses A15 to A0. As A0 to A9 are decoded internally, the
equation must only guarantee that addresses A10 to A15 must all be '0' and AEN must also be
'0'.
IOCS# = !(!AEN & !A15 & !A14 & !A13 & !A12 & !A11 & !A10)
2. As the S1D13503 is capable of 16-bit I/O access, the IOCS16# bus signal must be driven exter-
nally to indicate such a cycle. As stated in the ISA specification, the IOCS16# is a straight
address decode without qualification.
IOCS16EN# = !(!IOCS# & A9 & A8 & !A7 & !A6 & !A5 & A4 & !A3 & !A2 & !A1)
5-2
PAL
SA1–15
3
A
6
B
74LS09
Figure 1-1 16-Bit ISA Bus Implementation
1
IOCS16EN
2
4
P
Q
5
G
74LS688
S1D13503
IOCS#
MEMCS#
VD0, VD7,
VD11–12,
AB0–19
VD14–15
BHE#
DB0–15
MEMW#
MEMR#
IOW#
IOR#
READY
LA23–17 (p0–6)
0000110 (q0–6)
S18A-G-003-01
V
CC
10kΩ