9 SRAM CONTROLLER (SRAMC)
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
9-1
SRAM Controller (SRAMC)
9
The S1C33L26 includes a bus controller that controls access to external memories. The bus controller consists of
an SRAM controller (SRAMC) for controlling the SRAM, an SDRAM controller (SDRAMC) for controlling the
SDRAM, and a data queue buffer (DQB) for efficiently reading from external memories.
The following describes the SRAMC. For information on the SDRAMC and DQB, see the “SDRAM Controller
(SDRAMC)” chapter.
SRAMC Module Overview
9.1
The SRAM controller (SRAMC) is a module for controlling the external bus. It can output up to six chip enable
signals and configure the access cycle and the connected device type for respective areas assigned to each chip en-
able signal. When the CPU or DMAC accesses an external memory space, the SRAMC reads/writes from/to the
connected memory or I/O device according to the defined access conditions.
The features of the SRAMC are described below.
• 26-bit address bus (maximum 64M-byte address space)
• 8-bit or 16-bit selectable data bus
• Up to six chip enable signals are available for connecting external devices.
• Supports connections to a Flash ROM, SRAM, and other devices such as an LCD driver.
• Programmable bus access wait cycle (0 to 15 cycles)
• Supports little endian access.
• Supports memory mapped I/O devices.
• Supports either A0 or BS (bus strobe) access type.
• Supports external wait requests via the #WAIT pin.
SRAMC Pins
9.2
Table 9.2.1 lists the pins used by the SRAMC.
2.1 SRAMC Pin List
Table 9.
Pin name
I/O
Qty
Function
D[15:0]
I/O
16
External data bus D[15:0]
A0/#BSL
O
1
External address bus A0 / Bus strobe (low byte) signal output
A[25:1]
O
25
External address bus A[25:1]
Note that the A[25:24] pins do not exist in the TQFP15-128pin model.
#CE10, #CE9, #CE8, #CE7,
#CE5, #CE4
O
6
Chip enable signal outputs
#RD
O
1
Read signal output
#WRL
O
1
Write (low byte) signal output
#WRH/#BSH
O
1
Write (high byte) signal / Bus strobe (high byte) signal output
#WAIT
I
1
External wait request signal input
Notes: • Some of the bus control pins listed above are shared with general-purpose I/O ports and they
may be configured for I/O ports at initial reset. Before the SRAMC signals assigned to these
pins can be used, the functions of these pins must be switched for the SRAMC by setting each
corresponding port function select bit.
For details on how to switch over the pin functions, see the “I/O Ports (GPIO)” chapter.
• The bus control signals can be pulled up or forcibly driven low via software. For more informa-
tion, see the “I/O Ports (GPIO)” chapter.