DS80C400 Maxim, DS80C400 Datasheet - Page 72

• Manufacturer Part Number: DS80C400
• Description: The DS80C400 network microcontroller offers the highest integration available in an 8051 device
• Manufacturer: Maxim

Serial Loader
The serial loader function implemented by the firmware can be invoked by leaving the serial loader pin (P1.7) at
logic 1 during the boot sequence. When this condition is found, the ROM monitors the RXD0 pin for reception of
the <CR> character (0Dh) at a supported baud rate. The serial loader function uses hardware serial port 0 in mode
1 (asynchronous, one start bit, eight data bits, no parity, and one stop bit in full duplex). The serial loader can
automatically detect certain baud rates and configure itself to that speed. The equation below is used to calculate
the nearest integer-reload value for Timer 2 (used for serial port 0 baud rate generation) based on the external
clock frequency and desired baud rate. The calculated (nearest integer) RCAP2H, RCAP2L reload value may not
result in an exact baud rate match. The calculated reload value and clock frequency can be used in the equation to
solve for the baud rate configurable by the DS80C400. It is advised that the baud rate mismatch be no greater than
±2.5% to maintain reliable communication. The functionality was designed to work for clock rates from 3.680MHz to
75.000MHz and baud rates from 2400 to 115,200.
For example, suppose an 18MHz crystal is being used and a 19,200 baud rate is desired. The above equation
yields a nearest integer reload value of FFE3h. This reload value results in a true baud rate of 19396.6 (+1% error).
Once a supported baud rate has been detected, the DS80C400 transmits an ASCII text banner containing
copyright information and prompt for command entry. At this point, the user can issue any of the supported serial
loader commands. A summary of the supported serial loader commands can be seen in
description of each command and further information pertaining to the serial loader can be found in the High-Speed
Microcontroller User’s Guide: Network Microcontroller Supplement.
Table 17. Serial Loader Command Summary
NetBoot
The NetBoot process affords the user flexibility to download or update code remotely over the network. This
capability is quite powerful. Not only does it make firmware revisions trivial, but it also makes remote diagnostics
very practical. Also, since NetBoot can automatically reload the latest version of the user application code, the
system designer now has the option to select volatile SRAM for code storage.
For the NetBoot function to work, the DS80C400 ROM firmware must initialize certain hardware components and
create the environment needed to support the process. The NetBoot initialization code implements a primitive
memory manager, kicks off the task scheduler, and initializes the 1-Wire hardware, Ethernet driver, TCP/IP stack,
and socket layer.
Once the NetBoot initialization code has completed, the true network boot process can begin. The DS80C400
Ethernet MAC first must be assigned a physical address. Within the NetBoot process, the physical MAC address
can only be acquired through an external DS2502-E48 1-Wire chip. Hence, this 1-Wire chip, containing the MAC
address, is required for successful NetBoot operation.
COMMAND
H, ?
B
C
D
E
G
N
V
X
F
L
Z
Bank select
CRC-16 of memory range
Dump Intel hex data from selected bank
Exit the loader and try to execute code
Fill selected bank memory with hex data
Go: Start executing code at offset 0 in the current bank
Help: Display ROM version and current bank
Load Intel hex into memory
NetBoot
Verify memory against incoming hex
Execute code at a given offset in the current bank
Zap: Erase/clear the current bank.
RCAP2H, RCAP2L = 65,536 -
FUNCTION
72 of 97
Figure 14
Oscillator
32
shows the NetBoot code flow chart.
x
Clock
Baud
Frequency
Rate
Table
17. A detailed