71M6545 Datasheet, PDF (36/134 Pages) Maxim Integrated Products – Four-Quadrant Metering, Phase Metrology Processors Flash/RAM Size

Data Sheet 71M6545/H
PDS_6545_009
a DIO pin is configured as an output, the state of the pin can still be read by the MPU, for example when
counting pulses issued via DIO pins that are under CE control.
At power-up DIO0-14 are configured as inputs. It is necessary to write PORT_E = 1 (I/O RAM
0x270C[5]) to enable DIO0-DIO14. The default PORT_E = 0 blocks any momentary output
transient pulses that would otherwise occur when DIO0-14 are reset on power-up.
Clock Stretching (CKCON[2:0], SFR 0x8E)
The CKCON[2:0] field defines the stretch memory cycles that are used for MOVX instructions when
accessing external peripherals. The practical value of this register for the 71M6545/H is to guarantee
access to XRAM between CE, MPU, and SPI. The default setting of CKCON[2:0] (001) should not be
changed.
Table 15 shows how the signals of the External Memory Interface change when stretch values are set
from 0 to 7. The widths of the signals are counted in MPU clock cycles. The post-reset state of the
CKCON[2:0] field (001), which is shown in bold in the table, performs the MOVX instructions with a
stretch value equal to 1.
CKCON[2:0]
000
001
010
011
100
101
110
111
Table 15: Stretch Memory Cycle Width
Stretch
Value
Read Signal Width
memaddr memrd
Write Signal Width
memaddr memwr
0
1
1
2
1
1
2
2
3
1
2
3
3
4
2
3
4
4
5
3
4
5
5
6
4
5
6
6
7
5
6
7
7
8
6
7
8
8
9
7
2.4.6 Instruction Set
All instructions of the generic 8051 microcontroller are supported. A complete list of the instruction set
and of the associated op-codes is contained in the 71M654x Software User’s Guide (SUG).
2.4.7 UARTs
The 71M6545/H includes a UART (UART0) that can be programmed to communicate with a variety of
AMR modules and other external devices.
The UART is a dedicated 2-wire serial interface, which can communicate with an external host processor at
up to 38,400 bits/s (with MPU clock = 1.2288 MHz). The operation of the RX and TX UART0 pins is as
follows:
• UART0 RX: Serial input data are applied at this pin. Conforming to RS-232 standard, the bytes are
input LSB first.
• UART0 TX: This pin is used to output the serial data. The bytes are output LSB first.
The 71M6545/H has several UART-related registers for the control and buffering of serial data.
A single SFR register serves as both the transmit buffer and receive buffer (S0BUF, SFR 0x99 for UART0).
When written by the MPU, SxBUF acts as the transmit buffer, and when read by the MPU, it acts as the
receive buffer. Writing data to the transmit buffer starts the transmission by the UART. Received data are
available by reading from the receive buffer. The UART can simultaneously transmit and receive data.
36
© 2008–2011 Teridian Semiconductor Corporation
v1.0