4 MEMORY AND BUS
4-8
Seiko Epson Corporation
S1C17M20/M21/M22/M23/M24/M25
TECHNICAL MANUAL (Rev. 1.0)
4.5.1 System-Protect Function
The system-protect function protects control registers and bits from writings. They cannot be rewritten unless write
protection is removed by writing 0x0096 to the MSCPROT.PROT[15:0] bits. This function is provided to prevent
deadlock that may occur when a system-related register is altered by a runaway CPU. See “Control Registers” in
each peripheral circuit to identify the registers and bits with write protection.
Note: Once write protection is removed using the MSCPROT.PROT[15:0] bits, write enabled status is
maintained until write protection is applied again. After the registers/bits required have been al-
tered, apply write protection.
4.6 Control Registers
MISC System Protect Register
Register name
Bit
Bit name
Initial
Reset
R/W
Remarks
MSCPROT
15–0 PROT[15:0]
0x0000
H0
R/W –
Bits 15–0 PROT[15:0]
These bits protect the control registers related to the system against writings.
0x0096 (R/W):
Disable system protection
Other than 0x0096 (R/W): Enable system protection
While the system protection is enabled, any data will not be written to the affected control bits (bits
with “WP” or “R/WP” appearing in the R/W column).
MISC IRAM Size Register
Register name
Bit
Bit name
Initial
Reset
R/W
Remarks
MSCIRAMSZ
15–9 –
0x00
–
R
–
8
(reserved)
0
H0
R/WP Always set to 0.
7–3 –
0x04
–
R
–
2–0 IRAMSZ[2:0]
0x2
H0
R/WP
Bits 15–3 Reserved
Bits 2–0
IRAMSZ[2:0]
These bits set the internal RAM size that can be used.
Table 4.6.1 Internal RAM Size Selections
MSCIRAMSZ.IRAMSZ[2:0] bits
Internal RAM size
0x7–0x3
Reserved
0x2
2KB
0x1
1KB
0x0
512B
FLASHC Flash Read Cycle Register
Register name
Bit
Bit name
Initial
Reset
R/W
Remarks
FLASHCWAIT
15–9 –
0x00
–
R
–
8
(reserved)
0
H0
R/WP Always set to 0.
7–2 –
0x00
–
R
–
1–0 RDWAIT[1:0]
0x1
H0
R/WP
Bits 15–2 Reserved
Bits 1–0
RDWAIT[1:0]
These bits set the number of bus access cycles for reading from the Flash memory.