The Maxim MAX734 located at U11 is also a current-mode DC-DC converter. This device steps up the VCC voltage to +12.0 volts. This voltage output is supplied to provide a VPP option for Flash memory programming. The SHDN# input (pin 1) connects to a port pin (P1.1) on the processor through an inverter. At reset, SHDN# is driven low to disable the +12 volt signal. The output remains disabled until Port Pin 1.1 is programmed to a logic 0. When SHDN# is low, the output (pin 8) is VCC minus a diode drop. The evaluation board uses SmartVoltage Flash. To prevent unintentional writes to Flash, set jumpers E2 and E3 as indicated in Table 3-1.
3.6SERIAL INTERFACE
Connector P1 connects to your PC’s serial port. P1 interfaces pin-to-pin with a standard nine-pin RS-232 serial connector. Verify that the cable being used provides all signals required.
Table 3-3. P1 Host Serial Connector
P1 Connector | | Pin | Host RS-232 | Connection on |
| Nos. | Signal Name | Evaluation Board |
| | | | | |
| | | | | | | | |
| | | | | 1 | (CF) | DCD Data Carrier Detect | DTR P1-pin 4 |
| | | | | | | | |
| | | | | 2 | (BB) | RxD Receive Data | TxD of MAX561 |
| | | | | | | | |
| | | | | 3 | (BA) | TxD Transmit Data | RxD of MAX561 |
1 2 | 3 | 4 | 5 | | | | | |
| 4 | (CD) | DTR Data Terminal Ready | INIT |
| | | | | | | | |
6 | 7 | 8 | 9 | | 5 | (AB) | SG Signal Ground | Digital Ground |
| | | | |
| 6 | (CC) | DSR Data Set Ready | DTR P1-pin4 |
| | | | |
| | | | | | | |
| | | | | 7 (CA) | RTS Request To Send | CTS P1-pin8 |
| | | | | | | | |
| | | | | 8 | (CB) | CTS Clear To Send | RTS P1-pin7 |
| | | | | | | |
| | | | | 9 (CE) | RI Ring Indicator | Run Indicator |
| | | | | | | | |
Connector P2 is an additional serial port for user applications. Receive, Transmit, and Clear-to- Send are connected. Other connector pins are routed to test points on the board.
3-9
